diff --git a/.github/workflows/development.yaml b/.github/workflows/development.yaml
index 442515c..fe381c6 100644
--- a/.github/workflows/development.yaml
+++ b/.github/workflows/development.yaml
@@ -20,7 +20,7 @@ jobs:
       run: pip install flake8 && flake8
 
   test:
-    name: Test ${{ matrix.platform }} Python ${{ matrix.python-version }} 
+    name: Test on ${{ matrix.platform }} Python ${{ matrix.python-version }} 
     needs: lint
     strategy:
       max-parallel: 6
@@ -38,6 +38,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
+        pip install -r requirements_build.txt
         pip install -r requirements_test.txt
     - name: Build extensions
       run: make build_ext
@@ -52,7 +53,31 @@ jobs:
         git-branch: main
         parallel: true
 
-  finish:
+  examples:
+    name: Run examples on Python ${{ matrix.python-version }}
+    needs: lint
+    strategy:
+      max-parallel: 6
+      matrix:
+        python-version: [ "3.10", "3.11"]
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3  
+    - name: Set up Python ${{ matrix.python-version }}  
+      uses: actions/setup-python@v4
+      with:  
+        python-version: ${{ matrix.python-version }}
+    - name: Install package
+      run: make install-mpl
+    - name: Test examples
+      run: |
+        make install;
+        for i in examples/*.py; do
+            python $i && echo "$i is ok" || echo "$i fails";
+        done;
+
+  finish-coverage:
     name: Finalizing
     needs: test
     runs-on: ubuntu-latest
@@ -61,4 +86,4 @@ jobs:
       uses: coverallsapp/github-action@v2
       with:
         github-token: ${{ secrets.github_token }}
-        parallel-finished: true
+        parallel-finished: true 
diff --git a/examples/building_path.py b/examples/building_path.py
index d45e40f..68382ae 100644
--- a/examples/building_path.py
+++ b/examples/building_path.py
@@ -2,10 +2,11 @@
 Usage example showing how to map hexagons with different properties,
 calculate path and rendering result with a debug front end.
 """
+import matplotlib.pyplot as plt
+
 import geks
 from geks.front import FrontMPL
 
-
 # Create rectangular map of unblocked hexagons with pointy top
 default_value = {"price": 1, "blocked": False}
 hm = geks.RectHexmap(default_value, dims=(12, 8), flat=True)
@@ -22,34 +23,37 @@
 # Set rugged terrain by drawing a circle
 swamps = geks.hex_circle(geks.Hex((3, 0)), 1)
 for sw in swamps:
-    if sw in hm.map:
-        hm.map[sw]["price"] = 5
+    if sw in hm:
+        hm[sw]["price"] = 5
 
 # Draw hexagons according to their values
-for he, value in hm.map.items():
+for he, value in hm.items():
     mpl.plot_hex(
         he,
         fill=value["blocked"] or value["price"] > 1,
-        fillcolor="grey" if value["blocked"] else "lightgreen",
-        edgecolor="lightgrey",
+        facecolor="grey" if value["blocked"] else "lightgreen",
+        edgecolor="black",
     )
 
 # Highlight start and target hexagons
 start = geks.Hex((0, 0))
 target = geks.Hex((11, 2))
-mpl.plot_hex(start, fill=True, fillcolor="lightblue")
-mpl.plot_hex(target, fill=True, fillcolor="orange")
+mpl.plot_hex(start, facecolor="lightblue")
+mpl.plot_hex(target, facecolor="orange")
 
 # Build path
-path, nstep, nit = geks.dijkstra_path(
+path, nstep = geks.dijkstra_path(
     hm,
     start,
     target,
     distance=40,
-    block_func=lambda y, x: hm.map[x]["blocked"],  # walls condition
-    cost_func=lambda y, x: hm.map[x]["price"],  # cost of movement
+    block_func=lambda y, x: hm[x]["blocked"],  # walls condition
+    cost_func=lambda y, x: hm[x]["price"],  # cost of movement
 )
-mpl.plot_path(path, color="darkblue")
+mpl.plot_path(path, lw=2, color="darkblue")
 
-# Show results
-mpl.show()
+# Save resulting image
+mpl.fig.set_size_inches(10, 8)
+plt.gca().invert_yaxis()
+plt.autoscale(enable=True)
+plt.savefig("example.png")
diff --git a/examples/heights_and_rivers.py b/examples/heights_and_rivers.py
index 7a43d4a..53cdeba 100644
--- a/examples/heights_and_rivers.py
+++ b/examples/heights_and_rivers.py
@@ -1,6 +1,8 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
 import geks
 from geks.front import FrontMPL
-import numpy as np
 
 # Prepare height map
 hm = geks.RoundHexmap(0, 32)
@@ -24,6 +26,10 @@
 
 # Generate 10 rivers
 for edges in geks.generate_rivers(hm, 10, ocean_alt, source_min_alt):
-    mpl.plot_border(edges, color="#1F3C41", width=1.2)
+    mpl.plot_border(edges, color="#1F3C41", lw=1.2)
 
-mpl.show()
+# Save resulting image
+mpl.fig.set_size_inches(16, 16)
+plt.gca().invert_yaxis()
+plt.autoscale(enable=True)
+plt.savefig("example.png", transparent=True)
diff --git a/geks/__init__.py b/geks/__init__.py
index d97c4eb..745d593 100644
--- a/geks/__init__.py
+++ b/geks/__init__.py
@@ -1,26 +1,24 @@
 from .hexagon import Hex
+from .edge import HexEdge
 from .hexmap import RoundHexmap, RectHexmap
 from .layout import Layout
 from .pathfinding import dijkstra_scan, dijkstra_path
-from .heightmap import (
-    gen_heightmap,
-    fill_sinks_py,
-    fill_sinks_cy,
-    altitude_cdf,
-)
+from .heightmap import gen_heightmap, fill_sinks_cy, fill_sinks_py, \
+    altitude_cdf
 from .rivers import generate_rivers
 from .geometry import hex_distance, hex_line, hex_ring, hex_circle, hex_rotate
 
 __all__ = [
     "Hex",
+    "HexEdge",
     "RoundHexmap",
     "RectHexmap",
     "Layout",
     "dijkstra_scan",
     "dijkstra_path",
     "gen_heightmap",
-    "fill_sinks_py",
     "fill_sinks_cy",
+    "fill_sinks_py",
     "altitude_cdf",
     "generate_rivers",
     "hex_distance",
diff --git a/geks/front/front_mpl.py b/geks/front/front_mpl.py
index b04c02a..84bebab 100644
--- a/geks/front/front_mpl.py
+++ b/geks/front/front_mpl.py
@@ -16,6 +16,7 @@ def __init__(self, layout):
         self.layout = layout
         self.fig, self.ax = plt.subplots(1)
         self.ax.set_aspect("equal")
+        self.ax.set(frame_on=False)
 
         self.ax.set_yticklabels([])
         self.ax.set_xticklabels([])
@@ -27,26 +28,12 @@ def __init__(self, layout):
             lambda x: print(self.layout.pixel2hex((x.xdata, x.ydata)).round()),
         )
 
-    def show(self):
-        """Shows rendered objects with selected matplotlib backend"""
-        plt.gca().invert_yaxis()
-        plt.autoscale(enable=True)
-        plt.show()
-
-    def plot_hex(
-        self, he, fill=False, fillcolor=None, edgecolor=None, alpha=1
-    ):
+    def plot_hex(self, he, **kwargs):
         """Renders hexagon"""
-        patch = Polygon(
-            self.layout.hex_corners(he),
-            fill=fill,
-            facecolor=fillcolor,
-            edgecolor=edgecolor,
-            alpha=alpha,
-        )
+        patch = Polygon(self.layout.hex_corners(he), **kwargs)
         self.ax.add_patch(patch)
 
-    def plot_hexmap(self, hm, colors, ignore_func=lambda x: False):
+    def plot_hexmap(self, hm, colors, ignore_func=lambda x: False, **kwargs):
         """Renders collection of hexagons"""
         cmap = LinearSegmentedColormap.from_list("terrain", colors)
 
@@ -54,34 +41,40 @@ def plot_hexmap(self, hm, colors, ignore_func=lambda x: False):
         for he, val in hm.items():
             if ignore_func(he):
                 continue
-            patch = Polygon(self.layout.hex_corners(he), color=cmap(val))
+            patch = Polygon(
+                self.layout.hex_corners(he),
+                color=cmap(val),
+                **kwargs
+            )
             patches.append(patch)
         pc = PatchCollection(patches, match_original=True)
         self.ax.add_collection(pc)
 
-    def plot_path(self, path, width=1, color=None):
+    def plot_path(self, path, **kwargs):
         """Renders a trace connecting given hexagons"""
         if not path or len(path) < 2:
             return
         xy = np.array([self.layout.hex2pixel(he) for he in path])
-        self.ax.plot(xy[:, 0], xy[:, 1], linewidth=width, color=color)
+        self.ax.plot(xy[:, 0], xy[:, 1], **kwargs)
 
-    def plot_edge(self, he, di, width=1, color=None):
+    def plot_edge(self, he, di, **kwargs):
         """Renders hexagon's edge in given direction"""
         edge = self.layout.hex_edge(he, di)
-        self.ax.plot(edge[:, 0], edge[:, 1], color=color, linewidth=width)
+        self.ax.plot(edge[:, 0], edge[:, 1], **kwargs)
 
-    def plot_border(self, edges, width=1, color=None):
+    def plot_border(self, edges, **kwargs):
         if len(edges) == 0:
             return
         xy = np.array([self.layout.hex_edge(e) for e in edges])
         xy = xy.reshape(-1, xy.shape[-1])
         xy = np.delete(xy, np.arange(1, xy.shape[0] - 1, 2), axis=0)
-        self.ax.plot(xy[:, 0], xy[:, 1], linewidth=width, color=color)
+        self.ax.plot(xy[:, 0], xy[:, 1], **kwargs)
 
-    def label(self, he, text, color=None):
+    def label(self, he, text, **kwargs):
         """Renders text inside hexagon"""
         pos = self.layout.hex2pixel(he)
-        self.ax.annotate(
-            text, pos, ha="center", va="center", color=color
-        )
+        if "ha" not in kwargs:
+            kwargs["ha"] = "center"
+        if "va" not in kwargs:
+            kwargs["va"] = "center"
+        self.ax.annotate(text, pos, **kwargs)
diff --git a/geks/hexmap.py b/geks/hexmap.py
index f4012f8..7f1e60d 100644
--- a/geks/hexmap.py
+++ b/geks/hexmap.py
@@ -130,7 +130,7 @@ def center(self):
         """Returns central hexagon."""
         center = self.dims // 2
         if self.flat:
-            pass
+            center[1] -= center[0] // 2
         else:
             center[0] -= center[1] // 2
         return Hex(center)
diff --git a/geks/rivers.py b/geks/rivers.py
index cd6c7dc..9493c27 100644
--- a/geks/rivers.py
+++ b/geks/rivers.py
@@ -77,8 +77,7 @@ def generate_rivers(
     ocean_alt,
     source_min_alt,
     source_min_dist=2,
-    edgify=True,
-    curv=None,
+    curv=None
 ):
     """
     Generates rivers from the given minimal altitude to the ocean level or the
@@ -96,8 +95,6 @@ def generate_rivers(
         Minimal altitude of river sources
     source_min_dist : int, default: 2
         Minimal distance between river sources
-    edgify : bool, default: True
-        Plot rivers through hexagons' edges
     curv : int or None, default: None
         If None, edgified river curvature increases as river gets closer to
         the ocean. Otherwise curvature will be fixed, the higher the value is.
@@ -120,9 +117,6 @@ def generate_rivers(
         pool = [he for he in pool if he not in busy]
         it += 1
 
-    if not edgify:
-        return rivers
-
     # Direct rivers through edges of hexagons and handle mergers
     all_edges = []
     for river in rivers:
diff --git a/requirements_test.txt b/requirements_test.txt
index de04b77..d14e63a 100644
--- a/requirements_test.txt
+++ b/requirements_test.txt
@@ -1,4 +1,2 @@
-Cython>=3.0.2
-numpy>=1.23.5
 pytest>=7.4.0
 pytest-cov>=4.1.0
diff --git a/test/test_borders.py b/test/test_borders.py
new file mode 100644
index 0000000..13facea
--- /dev/null
+++ b/test/test_borders.py
@@ -0,0 +1,11 @@
+import geks
+
+
+def test_edge_equal():
+    he = geks.Hex((0, 0))
+    di = geks.Hex((1, 1))
+    edge0 = geks.HexEdge(he, di, 1)
+
+    ne = he + di
+    edge1 = geks.HexEdge(ne, he - ne, 1)
+    assert edge0 == edge1
diff --git a/test/test_rivers.py b/test/test_rivers.py
index 5f61b7a..8dbe238 100644
--- a/test/test_rivers.py
+++ b/test/test_rivers.py
@@ -1,14 +1,7 @@
 import geks
 
 
-def test_river_centers():
-    hm = geks.RectHexmap(None, (40, 20))
-    geks.gen_heightmap(hm)
-    geks.fill_sinks_cy(hm)
-    geks.generate_rivers(hm, 5, -1, 150, edgify=False)
-
-
-def test_river_edges():
+def test_river():
     hm = geks.RectHexmap(None, (40, 20))
     geks.gen_heightmap(hm)
     geks.fill_sinks_cy(hm)