diff --git a/.pylintrc b/.pylintrc
index 242f3c7..01e9428 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -133,7 +133,7 @@ module-rgx=(([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+))$
 const-rgx=(([A-Za-z_][A-Za-z0-9_]*)|(__.*__))$
 
 # Regular expression which should only match correct class names
-class-rgx=[a-zA-Z_][a-zA-Z0-9]+$
+class-rgx=[a-zA-Z_][a-zA-Z0-9_]+$
 
 # Regular expression which should only match correct function names
 function-rgx=[a-z_][a-z0-9_]{2,30}$
@@ -200,7 +200,7 @@ max-args=20
 ignored-argument-names=_.*
 
 # Maximum number of locals for function / method body
-max-locals=15
+max-locals=30
 
 # Maximum number of return / yield for function / method body
 max-returns=6
diff --git a/demo/moulinrouge/__init__.py b/demo/moulinrouge/__init__.py
index 3e4a8e3..e6b1e39 100644
--- a/demo/moulinrouge/__init__.py
+++ b/demo/moulinrouge/__init__.py
@@ -103,7 +103,8 @@ def create_app():
 
     @app.route("/all")
     @app.route("/all/style=<style>")
-    def all(style=DefaultStyle):
+    @app.route("/all/interpolate=<interpolate>")
+    def all(style='default', interpolate=None):
         width, height = 600, 400
         data = random.randrange(1, 10)
         order = random.randrange(1, 10)
@@ -119,6 +120,7 @@ def create_app():
         config.height = height
         config.fill = bool(random.randrange(0, 2))
         config.human_readable = True
+        config.interpolate = interpolate
         config.style = styles[style]
         config.x_labels = [random_label() for i in range(data)]
         svgs = []
diff --git a/pygal/config.py b/pygal/config.py
index 7438ffd..0057f80 100644
--- a/pygal/config.py
+++ b/pygal/config.py
@@ -31,7 +31,6 @@ class FontSizes(object):
 
 class Config(object):
     """Class holding config values"""
-    _horizontal = False
 
     #: Graph width
     width = 800
diff --git a/pygal/graph/__init__.py b/pygal/graph/__init__.py
index 98db20d..e7c4acb 100644
--- a/pygal/graph/__init__.py
+++ b/pygal/graph/__init__.py
@@ -16,3 +16,7 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Graph modules
+
+"""
diff --git a/pygal/graph/bar.py b/pygal/graph/bar.py
index 76efa61..3307ba3 100644
--- a/pygal/graph/bar.py
+++ b/pygal/graph/bar.py
@@ -16,14 +16,23 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Bar chart
+
+"""
+
 from __future__ import division
 from pygal.graph.graph import Graph
-from pygal.util import swap, ident
+from pygal.util import swap, ident, compute_scale
 
 
 class Bar(Graph):
     """Bar graph"""
 
+    def __init__(self, *args, **kwargs):
+        self._x_ranges = None
+        super(Bar, self).__init__(*args, **kwargs)
+
     def bar(self, serie_node, serie, values, stack_vals=None):
         """Draw a bar graph for a serie"""
         # value here is a list of tuple range of tuple coord
@@ -31,7 +40,7 @@ class Bar(Graph):
         def view(rng):
             """Project range"""
             t, T = rng
-            fun = swap if self._horizontal else ident
+            fun = swap if self.horizontal else ident
             return self.view(fun(t)), self.view(fun(T))
 
         bars = self.svg.node(serie_node['plot'], class_="bars")
@@ -52,12 +61,12 @@ class Bar(Graph):
             #
             # x and y are left range coords and X, Y right ones
             val = self._format(values[i][1][1])
-            if self._horizontal:
+            if self.horizontal:
                 x, y, X, Y = Y, X, y, x
             width = X - x
             padding = .1 * width
             inner_width = width - 2 * padding
-            if self._horizontal:
+            if self.horizontal:
                 height = self.view.x(0) - y
             else:
                 height = self.view.y(0) - y
@@ -93,11 +102,11 @@ class Bar(Graph):
                 str, (x + bar_inner_width / 2, y + height / 2))
             self.svg.node(bar, 'desc',
                           class_="x centered"
-            ).text = tooltip_positions[int(self._horizontal)]
+            ).text = tooltip_positions[int(self.horizontal)]
             self.svg.node(bar, 'desc',
                           class_="y centered"
-            ).text = tooltip_positions[int(not self._horizontal)]
-            if self._horizontal:
+            ).text = tooltip_positions[int(not self.horizontal)]
+            if self.horizontal:
                 x += .3 * self.value_font_size
                 y += height / 2
             else:
@@ -117,7 +126,8 @@ class Bar(Graph):
         x_step = len(self.series[0].values)
         x_pos = [x / x_step for x in range(x_step + 1)
         ] if x_step > 1 else [0, 1]  # Center if only one value
-        y_pos = self._compute_scale(self._box.ymin, self._box.ymax,
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic
         ) if not self.y_labels else map(float, self.y_labels)
 
         self._x_ranges = zip(x_pos, x_pos[1:])
diff --git a/pygal/graph/base.py b/pygal/graph/base.py
index 7e9e64e..431dadd 100644
--- a/pygal/graph/base.py
+++ b/pygal/graph/base.py
@@ -16,15 +16,20 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Base for pygal charts
+
+"""
+
 from __future__ import division
 import io
 from pygal.serie import Serie
 from pygal.view import Margin, Box
-from pygal.util import round_to_scale, cut, rad, humanize
+from pygal.util import get_text_box, get_texts_box, cut, rad, humanize
 from pygal.svg import Svg
 from pygal.config import Config
 from pygal.util import cached_property
-from math import log10, sin, cos, floor, ceil
+from math import sin, cos
 
 
 class BaseGraph(object):
@@ -32,11 +37,17 @@ class BaseGraph(object):
 
     def __init__(self, config=None, **kwargs):
         """Init the graph"""
+        self.horizontal = hasattr(self, 'horizontal') and self.horizontal
         self.config = config or Config()
         self.config(**kwargs)
         self.svg = Svg(self)
         self.series = []
-        self._x_labels = self._y_labels = None
+        self._x_labels = None
+        self._y_labels = None
+        self._box = None
+        self.nodes = {}
+        self.margin = None
+        self.view = None
 
     def add(self, title, values):
         """Add a serie to this graph"""
@@ -58,69 +69,6 @@ class BaseGraph(object):
         """Return the value formatter for this graph"""
         return humanize if self.human_readable else str
 
-    def _compute_logarithmic_scale(self, min_, max_):
-        """Compute an optimal scale for logarithmic"""
-        min_order = int(floor(log10(min_)))
-        max_order = int(ceil(log10(max_)))
-        positions = []
-        amplitude = max_order - min_order
-        if amplitude <= 1:
-            return []
-        detail = 10.
-        while amplitude * detail < 20:
-            detail *= 2
-        while amplitude * detail > 50:
-            detail /= 2
-        for order in range(min_order, max_order + 1):
-            for i in range(int(detail)):
-                tick = (10 * i / detail or 1) * 10 ** order
-                tick = round_to_scale(tick, tick)
-                if min_ <= tick <= max_ and tick not in positions:
-                    positions.append(tick)
-        return positions
-
-    def _compute_scale(self, min_, max_, min_scale=4, max_scale=20):
-        """Compute an optimal scale between min and max"""
-        if min_ == 0 and max_ == 0:
-            return [0]
-        if max_ - min_ == 0:
-            return [min_]
-        if self.logarithmic:
-            log_scale = self._compute_logarithmic_scale(min_, max_)
-            if log_scale:
-                return log_scale
-                # else we fallback to normal scalling
-        order = round(log10(max(abs(min_), abs(max_)))) - 1
-        while (max_ - min_) / (10 ** order) < min_scale:
-            order -= 1
-        step = float(10 ** order)
-        while (max_ - min_) / step > max_scale:
-            step *= 2.
-        positions = []
-        position = round_to_scale(min_, step)
-        while position < (max_ + step):
-            rounded = round_to_scale(position, step)
-            if min_ <= rounded <= max_:
-                if rounded not in positions:
-                    positions.append(rounded)
-            position += step
-        if len(positions) < 2:
-            return [min_, max_]
-        return positions
-
-    def _text_len(self, lenght, fs):
-        """Approximation of text length"""
-        return lenght * 0.6 * fs
-
-    def _get_text_box(self, text, fs):
-        """Approximation of text bounds"""
-        return (fs, self._text_len(len(text), fs))
-
-    def _get_texts_box(self, texts, fs):
-        """Approximation of multiple texts bounds"""
-        max_len = max(map(len, texts))
-        return (fs, self._text_len(max_len, fs))
-
     def _compute(self):
         """Initial computations to draw the graph"""
 
@@ -130,16 +78,16 @@ class BaseGraph(object):
     def _compute_margin(self):
         """Compute graph margins from set texts"""
         if self.show_legend:
-            h, w = self._get_texts_box(
+            h, w = get_texts_box(
                 cut(self.series, 'title'), self.legend_font_size)
             self.margin.right += 10 + w + self.legend_box_size
 
         if self.title:
-            h, w = self._get_text_box(self.title, self.title_font_size)
+            h, w = get_text_box(self.title, self.title_font_size)
             self.margin.top += 10 + h
 
         if self._x_labels:
-            h, w = self._get_texts_box(
+            h, w = get_texts_box(
                 cut(self._x_labels), self.label_font_size)
             self.margin.bottom += 10 + max(
                 w * sin(rad(self.x_label_rotation)), h)
@@ -148,7 +96,7 @@ class BaseGraph(object):
                     w * cos(rad(self.x_label_rotation)),
                     self.margin.right)
         if self._y_labels:
-            h, w = self._get_texts_box(
+            h, w = get_texts_box(
                 cut(self._y_labels), self.label_font_size)
             self.margin.left += 10 + max(
                 w * cos(rad(self.y_label_rotation)), h)
diff --git a/pygal/graph/graph.py b/pygal/graph/graph.py
index d6a9d7a..d0bd027 100644
--- a/pygal/graph/graph.py
+++ b/pygal/graph/graph.py
@@ -16,10 +16,17 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Commmon graphing functions
+
+"""
+
 from __future__ import division
+from pygal.interpolate import interpolation
 from pygal.graph.base import BaseGraph
 from pygal.view import View, LogView
 from pygal.util import is_major
+from math import isnan, pi
 
 
 class Graph(BaseGraph):
@@ -43,49 +50,51 @@ class Graph(BaseGraph):
 
     def _make_graph(self):
         """Init common graph svg structure"""
-        self.graph_node = self.svg.node(
+        self.nodes['graph'] = self.svg.node(
             class_='graph %s-graph' % self.__class__.__name__.lower())
-        self.svg.node(self.graph_node, 'rect',
+        self.svg.node(self.nodes['graph'], 'rect',
                   class_='background',
                   x=0, y=0,
                   width=self.width,
                   height=self.height)
-        self.plot = self.svg.node(
-            self.graph_node, class_="plot",
+        self.nodes['plot'] = self.svg.node(
+            self.nodes['graph'], class_="plot",
             transform="translate(%d, %d)" % (
                 self.margin.left, self.margin.top))
-        self.svg.node(self.plot, 'rect',
+        self.svg.node(self.nodes['plot'], 'rect',
                   class_='background',
                   x=0, y=0,
                   width=self.view.width,
                   height=self.view.height)
-        self.overlay = self.svg.node(
-            self.graph_node, class_="plot overlay",
+        self.nodes['overlay'] = self.svg.node(
+            self.nodes['graph'], class_="plot overlay",
             transform="translate(%d, %d)" % (
                 self.margin.left, self.margin.top))
-        self.text_overlay = self.svg.node(
-            self.graph_node, class_="plot text-overlay",
+        self.nodes['text_overlay'] = self.svg.node(
+            self.nodes['graph'], class_="plot text-overlay",
             transform="translate(%d, %d)" % (
                 self.margin.left, self.margin.top))
-        tooltip_overlay = self.svg.node(
-            self.graph_node, class_="plot tooltip-overlay",
+        self.nodes['tooltip_overlay'] = self.svg.node(
+            self.nodes['graph'], class_="plot tooltip-overlay",
             transform="translate(%d, %d)" % (
                 self.margin.left, self.margin.top))
-        self.tooltip_node = self.svg.node(tooltip_overlay, id="tooltip",
-                                          transform='translate(0 0)')
+        self.nodes['tooltip'] = self.svg.node(
+            self.nodes['tooltip_overlay'],
+            id="tooltip",
+            transform='translate(0 0)')
 
-        self.svg.node(self.tooltip_node, 'rect',
+        self.svg.node(self.nodes['tooltip'], 'rect',
                       id="tooltip-box",
                       rx=5, ry=5,
         )
-        self.svg.node(self.tooltip_node, 'text')
+        self.svg.node(self.nodes['tooltip'], 'text')
 
     def _x_axis(self):
         """Make the x axis: labels and guides"""
         if not self._x_labels:
             return
 
-        axis = self.svg.node(self.plot, class_="axis x")
+        axis = self.svg.node(self.nodes['plot'], class_="axis x")
 
         if 0 not in [label[1] for label in self._x_labels]:
             self.svg.node(axis, 'path',
@@ -113,7 +122,7 @@ class Graph(BaseGraph):
         if not self._y_labels:
             return
 
-        axis = self.svg.node(self.plot, class_="axis y")
+        axis = self.svg.node(self.nodes['plot'], class_="axis y")
 
         if 0 not in [label[1] for label in self._y_labels]:
             self.svg.node(axis, 'path',
@@ -146,7 +155,7 @@ class Graph(BaseGraph):
         if not self.show_legend:
             return
         legends = self.svg.node(
-            self.graph_node, class_='legends',
+            self.nodes['graph'], class_='legends',
             transform='translate(%d, %d)' % (
                 self.margin.left + self.view.width + 10,
                 self.margin.top + 10))
@@ -174,7 +183,7 @@ class Graph(BaseGraph):
     def _title(self):
         """Make the title"""
         if self.title:
-            self.svg.node(self.graph_node, 'text', class_='title',
+            self.svg.node(self.nodes['graph'], 'text', class_='title',
                       x=self.margin.left + self.view.width / 2,
                       y=self.title_font_size + 10
             ).text = self.title
@@ -183,11 +192,34 @@ class Graph(BaseGraph):
         """Make serie node"""
         return dict(
             plot=self.svg.node(
-                self.plot,
+                self.nodes['plot'],
                 class_='series serie-%d color-%d' % (serie, serie)),
             overlay=self.svg.node(
-                self.overlay,
+                self.nodes['overlay'],
                 class_='series serie-%d color-%d' % (serie, serie)),
             text_overlay=self.svg.node(
-                self.text_overlay,
+                self.nodes['text_overlay'],
                 class_='series serie-%d color-%d' % (serie, serie)))
+
+    def _interpolate(self, ys, xs,
+                   polar=False, xy=False, xy_xmin=None, xy_rng=None):
+        """Make the interpolation"""
+        interpolate = interpolation(
+            xs, ys, kind=self.interpolate)
+        p = self.interpolation_precision
+        xmin = min(xs)
+        xmax = max(xs)
+        interpolateds = []
+        for i in range(int(p + 1)):
+            x = i / p
+            if polar:
+                x = .5 * pi + 2 * pi * x
+            elif xy:
+                x = xy_xmin + xy_rng * x
+            interpolated = float(interpolate(x))
+            if not isnan(interpolated) and xmin <= x <= xmax:
+                coord = (x, interpolated)
+                if polar:
+                    coord = tuple(reversed(coord))
+                interpolateds.append(coord)
+        return interpolateds
diff --git a/pygal/graph/horizontal.py b/pygal/graph/horizontal.py
index 900487c..cfce532 100644
--- a/pygal/graph/horizontal.py
+++ b/pygal/graph/horizontal.py
@@ -16,6 +16,10 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Horizontal graph
+
+"""
 from pygal.graph.graph import Graph
 from pygal.graph.bar import Bar
 from pygal.graph.stackedbar import StackedBar
@@ -25,13 +29,16 @@ class HorizontalGraph(Graph):
     """Horizontal graph"""
     def __init__(self, *args, **kwargs):
         self.first_pass = True
-        kwargs['_horizontal'] = True
+        self.horizontal = True
         super(HorizontalGraph, self).__init__(*args, **kwargs)
 
     def _compute(self):
         self.first_pass = False
+        # Stupid pylint
+        # pylint: disable-msg=E0203,W0201
         if self.first_pass and self.x_labels:
             self.x_labels = list(reversed(self.x_labels))
+        # pylint: enable-msg=W0201,E0203
         super(HorizontalGraph, self)._compute()
         self._x_labels, self._y_labels = self._y_labels, self._x_labels
         self._box.swap()
diff --git a/pygal/graph/line.py b/pygal/graph/line.py
index d7fb8b9..12ff509 100644
--- a/pygal/graph/line.py
+++ b/pygal/graph/line.py
@@ -16,17 +16,20 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Line chart
+
+"""
 from __future__ import division
 from pygal.graph.graph import Graph
-from pygal.util import cached_property
-from pygal.interpolate import interpolation
-from math import isnan
+from pygal.util import cached_property, compute_scale
 
 
 class Line(Graph):
     """Line graph"""
 
     def _get_value(self, values, i):
+        """Get the value formatted for tooltip"""
         return self._format(values[i][1])
 
     @cached_property
@@ -43,12 +46,14 @@ class Line(Graph):
                     if val[1] != None and (not self.logarithmic or val[1] > 0)]
 
     def _fill(self, values):
+        """Add extra values to fill the line"""
         zero = self.view.y(min(max(self.zero, self._box.ymin), self._box.ymax))
         return ([(values[0][0], zero)] +
                 values +
                 [(values[-1][0], zero)])
 
     def line(self, serie_node, serie):
+        """Draw the line serie"""
         view_values = map(self.view, serie.points)
         if self.show_dots:
             for i, (x, y) in enumerate(view_values):
@@ -88,21 +93,16 @@ class Line(Graph):
                 class_='line reactive' + (' nofill' if not self.fill else ''))
 
     def _compute(self):
-        self._x_pos = [x / float(self._len - 1) for x in range(self._len)
+        x_pos = [x / float(self._len - 1) for x in range(self._len)
         ] if self._len != 1 else [.5]  # Center if only one value
         for serie in self.series:
             if not hasattr(serie, 'points'):
                 serie.points = [
-                    (self._x_pos[i], v)
+                    (x_pos[i], v)
                     for i, v in enumerate(serie.values)]
                 if self.interpolate:
-                    interpolate = interpolation(
-                        self._x_pos, serie.values, kind=self.interpolate)
-                    p = float(self.interpolation_precision)
-                    serie.interpolated = [
-                        (x / p, float(interpolate(x / p)))
-                        for x in range(int(p + 1))
-                        if not isnan(float(interpolate(x / p)))]
+                    serie.interpolated = self._interpolate(serie.values, x_pos)
+
         if self.include_x_axis:
             self._box.ymin = min(min(self._values), 0)
             self._box.ymax = max(max(self._values), 0)
@@ -110,11 +110,12 @@ class Line(Graph):
             self._box.ymin = min(self._values)
             self._box.ymax = max(self._values)
 
-        self._y_pos = self._compute_scale(self._box.ymin, self._box.ymax
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic
         ) if not self.y_labels else map(float, self.y_labels)
 
-        self._x_labels = self.x_labels and zip(self.x_labels, self._x_pos)
-        self._y_labels = zip(map(self._format, self._y_pos), self._y_pos)
+        self._x_labels = self.x_labels and zip(self.x_labels, x_pos)
+        self._y_labels = zip(map(self._format, y_pos), y_pos)
 
     def _plot(self):
         for serie in self.series:
diff --git a/pygal/graph/pie.py b/pygal/graph/pie.py
index 7ef5453..7456fde 100644
--- a/pygal/graph/pie.py
+++ b/pygal/graph/pie.py
@@ -16,6 +16,11 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Pie chart
+
+"""
+
 from __future__ import division
 from pygal.graph.graph import Graph
 from math import cos, sin, pi
@@ -31,6 +36,7 @@ class Pie(Graph):
 
     def slice(self, serie_node, start_angle, angle, perc,
             small=False):
+        """Make a serie slice"""
         val = '{0:.2%}'.format(perc)
         slices = self.svg.node(serie_node['plot'], class_="slices")
         slice_ = self.svg.node(slices, class_="slice")
@@ -51,16 +57,16 @@ class Pie(Graph):
         else:
             absolute_project = lambda rho, theta: fmt(
                 diff(center, project(rho, theta)))
-            to1 = absolute_project(r, start_angle)
-            to2 = absolute_project(r, start_angle + angle)
-            to3 = absolute_project(small_r, start_angle + angle)
-            to4 = absolute_project(small_r, start_angle)
+            to = [absolute_project(r, start_angle),
+                  absolute_project(r, start_angle + angle),
+                  absolute_project(small_r, start_angle + angle),
+                  absolute_project(small_r, start_angle)]
             self.svg.node(slice_, 'path',
                           d='M%s A%s 0 %d 1 %s L%s A%s 0 %d 0 %s z' % (
-                              to1,
-                              get_radius(r), int(angle > pi), to2,
-                              to3,
-                              get_radius(small_r), int(angle > pi), to4),
+                              to[0],
+                              get_radius(r), int(angle > pi), to[1],
+                              to[2],
+                              get_radius(small_r), int(angle > pi), to[3]),
                           class_='slice reactive tooltip-trigger')
         self.svg.node(slice_, 'desc', class_="value").text = val
         tooltip_position = map(
@@ -97,7 +103,7 @@ class Pie(Graph):
                 angle, sum(serie.values) / total)
             if len(serie.values) > 1:
                 small_current_angle = current_angle
-                for i, val in enumerate(serie.values):
+                for val in serie.values:
                     small_angle = 2 * pi * val / total
                     self.slice(
                         self._serie(serie.index),
diff --git a/pygal/graph/radar.py b/pygal/graph/radar.py
index 0284961..97ecfc2 100644
--- a/pygal/graph/radar.py
+++ b/pygal/graph/radar.py
@@ -16,17 +16,26 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Radar chart
+
+"""
+
 from __future__ import division
 from pygal.graph.line import Line
 from pygal.view import PolarView
-from pygal.util import deg, cached_property
-from pygal.interpolate import interpolation
+from pygal.util import deg, cached_property, compute_scale
 from math import cos, pi
 
 
 class Radar(Line):
     """Kiviat graph"""
 
+    def __init__(self, *args, **kwargs):
+        self.x_pos = None
+        self._rmax = None
+        super(Radar, self).__init__(*args, **kwargs)
+
     def _fill(self, values):
         return values
 
@@ -51,17 +60,17 @@ class Radar(Line):
         if not self._x_labels:
             return
 
-        axis = self.svg.node(self.plot, class_="axis x web")
-        format = lambda x: '%f %f' % x
+        axis = self.svg.node(self.nodes['plot'], class_="axis x web")
+        format_ = lambda x: '%f %f' % x
         center = self.view((0, 0))
         r = self._rmax
         for label, theta in self._x_labels:
             guides = self.svg.node(axis, class_='guides')
             end = self.view((r, theta))
             self.svg.node(guides, 'path',
-                      d='M%s L%s' % (format(center), format(end)),
+                      d='M%s L%s' % (format_(center), format_(end)),
                       class_='line')
-            r_txt = (1 - self._box.__class__._margin) * self._box.ymax
+            r_txt = (1 - self._box.__class__.margin) * self._box.ymax
             pos_text = self.view((r_txt, theta))
             text = self.svg.node(guides, 'text',
                       x=pos_text[0],
@@ -72,21 +81,21 @@ class Radar(Line):
             if cos(angle) < 0:
                 angle -= pi
             text.attrib['transform'] = 'rotate(%f %s)' % (
-                deg(angle), format(pos_text))
+                deg(angle), format_(pos_text))
 
     def _y_axis(self):
         if not self._y_labels:
             return
 
-        axis = self.svg.node(self.plot, class_="axis y web")
+        axis = self.svg.node(self.nodes['plot'], class_="axis y web")
 
         for label, r in reversed(self._y_labels):
             guides = self.svg.node(axis, class_='guides')
             self.svg.line(
-                guides, [self.view((r, theta)) for theta in self._x_pos],
+                guides, [self.view((r, theta)) for theta in self.x_pos],
                 close=True,
                 class_='guide line')
-            x, y = self.view((r, self._x_pos[0]))
+            x, y = self.view((r, self.x_pos[0]))
             self.svg.node(guides, 'text',
                              x=x - 5,
                              y=y
@@ -94,37 +103,34 @@ class Radar(Line):
 
     def _compute(self):
         delta = 2 * pi / self._len
-        self._x_pos = [.5 * pi + i * delta for i in range(self._len + 1)]
+        x_pos = [.5 * pi + i * delta for i in range(self._len + 1)]
         for serie in self.series:
             vals = list(serie.values)
             vals.append(vals[0])
             vals = [val if val != None else 0 for val in vals]
             serie.points = [
-                (v, self._x_pos[i])
+                (v, x_pos[i])
                 for i, v in enumerate(vals)]
             if self.interpolate:
                 extend = 2
                 extended_x_pos = (
                     [.5 * pi + i * delta for i in range(-extend, 0)] +
-                    self._x_pos +
+                    x_pos +
                     [.5 * pi + i * delta for i in range(
                         self._len + 1, self._len + 1 + extend)])
                 extended_vals = vals[-extend:] + vals + vals[:extend]
-                interpolate = interpolation(
-                    extended_x_pos, extended_vals, kind=self.interpolate)
-                serie.interpolated = []
-                p = self.interpolation_precision
-                for s in range(int(p + 1)):
-                    x = .5 * pi + 2 * pi * (s / p)
-                    serie.interpolated.append((float(interpolate(x)), x))
-
-        self._box._margin *= 2
+                serie.interpolated = self._interpolate(
+                    extended_vals, extended_x_pos, polar=True)
+
+        self._box.margin *= 2
         self._box.xmin = self._box.ymin = 0
         self._box.xmax = self._box.ymax = self._rmax = max(self._values)
 
-        self._y_pos = self._compute_scale(
-            self._box.ymin, self._box.ymax, max_scale=8
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic, max_scale=8
         ) if not self.y_labels else map(int, self.y_labels)
-        self._x_labels = self.x_labels and zip(self.x_labels, self._x_pos)
-        self._y_labels = zip(map(self._format, self._y_pos), self._y_pos)
+        self._x_labels = self.x_labels and zip(self.x_labels, x_pos)
+        self._y_labels = zip(map(self._format, y_pos), y_pos)
         self._box.xmin = self._box.ymin = - self._box.ymax
+
+        self.x_pos = x_pos
diff --git a/pygal/graph/stackedbar.py b/pygal/graph/stackedbar.py
index defdc74..48092a5 100644
--- a/pygal/graph/stackedbar.py
+++ b/pygal/graph/stackedbar.py
@@ -16,8 +16,14 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Stacked Bar chart
+
+"""
+
 from __future__ import division
 from pygal.graph.bar import Bar
+from pygal.util import compute_scale
 
 
 class StackedBar(Bar):
@@ -34,12 +40,12 @@ class StackedBar(Bar):
 
         self._box.ymin, self._box.ymax = (
             min(min(negative_vals), 0), max(max(positive_vals), 0))
-        self._length = len(self.series[0].values)
 
-        x_pos = [x / self._length
-                 for x in range(self._length + 1)
-             ] if self._length > 1 else [0, 1]  # Center if only one value
-        y_pos = self._compute_scale(self._box.ymin, self._box.ymax
+        x_pos = [x / self._len
+                 for x in range(self._len + 1)
+             ] if self._len > 1 else [0, 1]  # Center if only one value
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic
         ) if not self.y_labels else map(float, self.y_labels)
         self._x_ranges = zip(x_pos, x_pos[1:])
 
@@ -48,7 +54,7 @@ class StackedBar(Bar):
         self._y_labels = zip(map(self._format, y_pos), y_pos)
 
     def _plot(self):
-        stack_vals = [[0, 0] for i in range(self._length)]
+        stack_vals = [[0, 0] for i in range(self._len)]
         for serie in self.series:
             serie_node = self._serie(serie.index)
             stack_vals = self.bar(
diff --git a/pygal/graph/stackedline.py b/pygal/graph/stackedline.py
index 513d5cd..410735d 100644
--- a/pygal/graph/stackedline.py
+++ b/pygal/graph/stackedline.py
@@ -16,17 +16,24 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Stacked Line chart
+
+"""
+
 from pygal.graph.line import Line
-from pygal.interpolate import interpolation
-from math import isnan
 from itertools import izip_longest
 
 
 class StackedLine(Line):
     """Stacked Line graph"""
 
+    def __init__(self, *args, **kwargs):
+        self._previous_line = None
+        super(StackedLine, self).__init__(*args, **kwargs)
+
     def _fill(self, values):
-        if not hasattr(self, '_previous_line'):
+        if not self._previous_line:
             self._previous_line = values
             return super(StackedLine, self)._fill(values)
         new_values = values + list(reversed(self._previous_line))
@@ -34,7 +41,7 @@ class StackedLine(Line):
         return new_values
 
     def _compute(self):
-        self._x_pos = [x / float(self._len - 1) for x in range(self._len)
+        x_pos = [x / float(self._len - 1) for x in range(self._len)
         ] if self._len != 1 else [.5]  # Center if only one value
         accumulation = [0] * self._len
         for serie in self.series:
@@ -43,14 +50,8 @@ class StackedLine(Line):
                                if val != None else 0
                                for val in serie.values], fillvalue=0))
             serie.points = [
-                (self._x_pos[i], v)
+                (x_pos[i], v)
                 for i, v in enumerate(accumulation)]
             if self.interpolate:
-                interpolate = interpolation(
-                    self._x_pos, accumulation, kind=self.interpolate)
-                p = float(self.interpolation_precision)
-                serie.interpolated = [
-                    (x / p, float(interpolate(x / p)))
-                    for x in range(int(p + 1))
-                    if not isnan(float(interpolate(x / p)))]
+                serie.interpolated = self._interpolate(accumulation, x_pos)
         return super(StackedLine, self)._compute()
diff --git a/pygal/graph/xy.py b/pygal/graph/xy.py
index b3cb000..80d280e 100644
--- a/pygal/graph/xy.py
+++ b/pygal/graph/xy.py
@@ -16,10 +16,14 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+XY Line graph
+
+"""
+
 from __future__ import division
+from pygal.util import compute_scale
 from pygal.graph.line import Line
-from pygal.interpolate import interpolation
-from math import isnan
 
 
 class XY(Line):
@@ -38,23 +42,17 @@ class XY(Line):
                  for val in serie.values
                  if val[1] != None]
         xmin = min(xvals)
+        xmax = max(xvals)
+        rng = (xmax - xmin)
 
         for serie in self.series:
             serie.points = serie.values
             if self.interpolate:
-                vals = zip(*serie.points)
-                interpolate = interpolation(
-                    vals[0], vals[1], kind=self.interpolate)
-                serie_xmin = min(vals[0])
-                serie_xmax = max(vals[0])
-                serie.interpolated = []
-                r = (max(xvals) - xmin)
-                p = self.interpolation_precision
-                for s in range(int(p + 1)):
-                    x = xmin + r * (s / p)
-                    if (serie_xmin <= x <= serie_xmax and not
-                        isnan(float(interpolate(x)))):
-                        serie.interpolated.append((x, float(interpolate(x))))
+                vals = zip(*sorted(serie.points, key=lambda x: x[0]))
+                serie.interpolated = self._interpolate(
+                    vals[1], vals[0], xy=True, xy_xmin=xmin, xy_rng=rng)
+                if not serie.interpolated:
+                    serie.interpolated = serie.values
 
         if self.interpolate:
             xvals = [val[0]
@@ -66,8 +64,10 @@ class XY(Line):
 
         self._box.xmin, self._box.xmax = min(xvals), max(xvals)
         self._box.ymin, self._box.ymax = min(yvals), max(yvals)
-        x_pos = self._compute_scale(self._box.xmin, self._box.xmax)
-        y_pos = self._compute_scale(self._box.ymin, self._box.ymax)
+        x_pos = compute_scale(
+        self._box.xmin, self._box.xmax, self.logarithmic)
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic)
 
         self._x_labels = zip(map(self._format, x_pos), x_pos)
         self._y_labels = zip(map(self._format, y_pos), y_pos)
diff --git a/pygal/svg.py b/pygal/svg.py
index 64c1a46..8ee1451 100644
--- a/pygal/svg.py
+++ b/pygal/svg.py
@@ -60,7 +60,7 @@ class Svg(object):
                 f.read(),
                 style=self.graph.style,
                 font_sizes=self.graph.font_sizes(),
-                hidden='y' if self.graph._horizontal else 'x')
+                hidden='y' if self.graph.horizontal else 'x')
             style.text = templ
 
     def add_script(self, js):
@@ -92,7 +92,7 @@ class Svg(object):
 
     def transposable_node(self, parent=None, tag='g', attrib=None, **extras):
         """Make a new svg node which can be transposed if horizontal"""
-        if self.graph._horizontal:
+        if self.graph.horizontal:
             for key1, key2 in (('x', 'y'), ('width', 'height')):
                 attr1 = extras.get(key1, None)
                 attr2 = extras.get(key2, None)
diff --git a/pygal/util.py b/pygal/util.py
index a1e2793..f0876de 100644
--- a/pygal/util.py
+++ b/pygal/util.py
@@ -23,7 +23,7 @@ Various utils
 
 from __future__ import division
 from decimal import Decimal
-from math import floor, pi, log, log10
+from math import floor, pi, log, log10, ceil
 ORDERS = u"yzafpnµm kMGTPEZY"
 
 
@@ -114,6 +114,74 @@ swap = lambda tuple_: tuple(reversed(tuple_))
 ident = lambda x: x
 
 
+def compute_logarithmic_scale(min_, max_):
+    """Compute an optimal scale for logarithmic"""
+    min_order = int(floor(log10(min_)))
+    max_order = int(ceil(log10(max_)))
+    positions = []
+    amplitude = max_order - min_order
+    if amplitude <= 1:
+        return []
+    detail = 10.
+    while amplitude * detail < 20:
+        detail *= 2
+    while amplitude * detail > 50:
+        detail /= 2
+    for order in range(min_order, max_order + 1):
+        for i in range(int(detail)):
+            tick = (10 * i / detail or 1) * 10 ** order
+            tick = round_to_scale(tick, tick)
+            if min_ <= tick <= max_ and tick not in positions:
+                positions.append(tick)
+    return positions
+
+
+def compute_scale(min_, max_, logarithmic=False, min_scale=4, max_scale=20):
+    """Compute an optimal scale between min and max"""
+    if min_ == 0 and max_ == 0:
+        return [0]
+    if max_ - min_ == 0:
+        return [min_]
+    if logarithmic:
+        log_scale = compute_logarithmic_scale(min_, max_)
+        if log_scale:
+            return log_scale
+            # else we fallback to normal scalling
+    order = round(log10(max(abs(min_), abs(max_)))) - 1
+    while (max_ - min_) / (10 ** order) < min_scale:
+        order -= 1
+    step = float(10 ** order)
+    while (max_ - min_) / step > max_scale:
+        step *= 2.
+    positions = []
+    position = round_to_scale(min_, step)
+    while position < (max_ + step):
+        rounded = round_to_scale(position, step)
+        if min_ <= rounded <= max_:
+            if rounded not in positions:
+                positions.append(rounded)
+        position += step
+    if len(positions) < 2:
+        return [min_, max_]
+    return positions
+
+
+def text_len(lenght, fs):
+    """Approximation of text length"""
+    return lenght * 0.6 * fs
+
+
+def get_text_box(text, fs):
+    """Approximation of text bounds"""
+    return (fs, text_len(len(text), fs))
+
+
+def get_texts_box(texts, fs):
+    """Approximation of multiple texts bounds"""
+    max_len = max(map(len, texts))
+    return (fs, text_len(max_len, fs))
+
+
 # Stolen from brownie http://packages.python.org/Brownie/
 class cached_property(object):
     """Optimize a static property"""
diff --git a/pygal/view.py b/pygal/view.py
index 9e865ec..f8c161e 100644
--- a/pygal/view.py
+++ b/pygal/view.py
@@ -45,7 +45,7 @@ class Margin(object):
 
 class Box(object):
     """Chart boundings"""
-    _margin = .02
+    margin = .02
 
     def __init__(self):
         self.xmin = self.ymin = 0
@@ -73,11 +73,11 @@ class Box(object):
         if not self.height:
             self.ymin -= .5
             self.ymax = self.ymin + 1
-        xmargin = self._margin * self.width
+        xmargin = self.margin * self.width
         self.xmin -= xmargin
         self.xmax += xmargin
         if with_margin:
-            ymargin = self._margin * self.height
+            ymargin = self.margin * self.height
             self.ymin -= ymargin
             self.ymax += ymargin