begone, line!

I set the political svgs to remove the divide thru russia at the antimeridian.  I'm a bit surprised I didn't try this sooner since it's just kind of an ugly erroneus line in most of my map projections.  unfortunately, the solution I found doesn't work for the physical maps.  that's a bit of a bummer for the tissot ellipse maps specificly.  however, it was most notable (and most potentially confusing) in the blank political templates, so I'm very glad that I fixd that.

src/zupplemental/compose_maps.py

@@ -115,7 +115,7 @@ def main():
 		'	<g transform="matrix(1,0,0,-1,180,90)">\n'
 		'		<rect class="water" x="-180" y="-90" width="360" height="180" />\n'
 		'		<g class="country">\n'
-		+ plot_political_shapes('ne_50m_admin_0_countries', trim_antarctica=True) +
+		+ plot_political_shapes('ne_50m_admin_0_countries', trim_antarctica=True, fuse_russia=True) +
 		'		</g>\n'
 		'		<g class="water">\n'
 		+ plot_shapes('ne_50m_lakes', max_rank=4) +
@@ -130,10 +130,10 @@ def main():
 		'	<g transform="matrix(1,0,0,-1,180,90)">\n'
 		'		<rect class="water" x="-180" y="-90" width="360" height="180" />\n'
 		'		<g class="country">\n'
-		+ plot_political_shapes('ne_110m_admin_0_countries', trim_antarctica=True, add_title=True,
-		                        mode="normal")
-		+ plot_political_shapes('ne_110m_admin_0_countries', trim_antarctica=True, add_title=True,
-		                        mode="circle", include_circles_from='ne_10m_admin_0_countries') +
+		+ plot_political_shapes('ne_110m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
+		                        add_title=True, mode="normal")
+		+ plot_political_shapes('ne_110m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
+		                        add_title=True, mode="circle", include_circles_from='ne_10m_admin_0_countries') +
 		'		</g>\n'
 		'		<g class="water">\n'
 		+ plot_shapes('ne_110m_lakes', max_rank=4) +
@@ -151,16 +151,17 @@ def main():
 		'	<g transform="matrix(1,0,0,-1,180,90)">\n'
 		'		<rect class="water" x="-180" y="-90" width="360" height="180" />\n'
 		'		<g class="province">\n'
-		+ plot_political_shapes('ne_50m_admin_1_states_provinces', trim_antarctica=True, add_title=True,
-		                        filter_field="adm0_a3", filter_values=a3_with_provinces) +
+		+ plot_political_shapes('ne_50m_admin_1_states_provinces', trim_antarctica=True, fuse_russia=True,
+		                        add_title=True, filter_field="adm0_a3", filter_values=a3_with_provinces) +
 		'		</g>\n'
 		'		<g class="country-outline">\n'
-		+ plot_shapes('ne_50m_admin_0_countries', trim_antarctica=True,
+		+ plot_shapes('ne_50m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
 		              filter_field="adm0_a3", filter_values=a3_with_provinces) +
 		'		</g>\n'
 		'		<g class="country">\n'
-		+ plot_political_shapes('ne_50m_admin_0_countries', trim_antarctica=True, add_title=True,
-		                        filter_field="adm0_a3", filter_values=a3_with_provinces, filter_mode="out") +
+		+ plot_political_shapes('ne_50m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
+		                        add_title=True, filter_field="adm0_a3", filter_values=a3_with_provinces,
+		                        filter_mode="out") +
 		'       </g>\n'
 		'		<g class="water">\n'
 		+ plot_shapes('ne_50m_lakes', max_rank=4) +
@@ -174,10 +175,12 @@ def main():
 		'	<g transform="matrix(1,0,0,-1,180,90)">\n'
 		'		<rect class="water" x="-180" y="-90" width="360" height="180" />\n'
 		'		<g class="country">\n'
-		+ plot_political_shapes('ne_10m_admin_0_countries', trim_antarctica=True, mode="normal") +
+		+ plot_political_shapes('ne_10m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
+		                        mode="normal") +
 		'		</g>\n'
 		'		<g class="thick-country-border">\n'
-		+ plot_political_shapes('ne_10m_admin_0_countries', trim_antarctica=True, mode="trace") +
+		+ plot_political_shapes('ne_10m_admin_0_countries', trim_antarctica=True, fuse_russia=True,
+		                        mode="trace") +
 		'		</g>\n'
 		'		<g class="river">\n'
 		+ plot_shapes('ne_10m_rivers_lake_centerlines', max_rank=5) +
@@ -193,7 +196,7 @@ def main():
 		+ plot_shapes('ne_10m_admin_0_boundary_lines_disputed_areas') +
 		'		</g>\n'
 		'		<g class="coastline">\n'
-		+ plot_shapes('ne_10m_coastline', trim_antarctica=True) +
+		+ plot_shapes('ne_10m_coastline', trim_antarctica=True, fuse_russia=True) +
 		'		</g>\n'
 		'		<g class="lake">\n'
 		+ plot_shapes('ne_10m_lakes', max_rank=4) +

src/zupplemental/generate_political_shapes.py

@@ -6,7 +6,7 @@ from numpy import pi, sqrt, cos, radians, inf
 from shapely import Polygon
 
 from helpers import plot, trim_edges, ShapeRecord, \
-	load_shapes_from_one_place_and_records_from_another, load_shaperecords
+	load_shapes_from_one_place_and_records_from_another, load_shaperecords, fuse_edges
 
 SIZE_CLASSES = [
 	'lg', 'md', 'sm', None, None, None]
@@ -49,7 +49,8 @@ ISO_A3_TO_A2 = {
 
 
 def plot_political_shapes(filename, mode="normal",
-                          trim_antarctica=False, add_title=False, include_circles_from=None,
+                          trim_antarctica=False, fuse_russia=False,
+                          add_title=False, include_circles_from=None,
                           filter_field: Optional[str] = None,
                           filter_values: Optional[list[Any]] = None, filter_mode="in") -> str:
 	""" it's like plot_shapes but it also can make circles and handles, like, dependencies and stuff
@@ -59,6 +60,7 @@ def plot_political_shapes(filename, mode="normal",
 	                        ID and clip to that existing shape, or
 	                        "circle" to do circles at the center of mass specificly for small countries
 	    :param trim_antarctica: whether to adjust antarctica's shape
+	    :param fuse_russia: whether to reattach the bit of Russia that's in the western hemisphere
 	    :param add_title: add mouseover text
 	    :param include_circles_from: an additional filename from which to borrow small objects. anything
 	                                 present in this shapefile but not in the main one will be included
@@ -91,8 +93,11 @@ def plot_political_shapes(filename, mode="normal",
 
 		# if it Antarctica, trim it
 		if trim_antarctica:
-			if record["sov_a3"] == 'ATA':
-				shape.points = trim_edges(shape.points, shape.parts)
+			if record["sov_a3"] == "ATA":
+				shape.points, shape.parts = trim_edges(shape.points, shape.parts)
+		if fuse_russia:
+			if record["sov_a3"] == "RUS":
+				shape.points, shape.parts = fuse_edges(shape.points, shape.parts)
 		sovereign_code = record["sov_a3"]
 		if sovereign_code in SOVEREIGN_CODES:
 			sovereign_code = SOVEREIGN_CODES[sovereign_code]  # convert US1 to USA

src/zupplemental/generate_shapes.py

@@ -1,12 +1,12 @@
 # read data from a shapefile into SVG format
 
-from helpers import plot, trim_edges, lengthen_edges, load_shaperecords
+from helpers import plot, trim_edges, lengthen_edges, load_shaperecords, fuse_edges
 
 
 def plot_shapes(
 		filename, max_rank=float('inf'), clazz=None,
-		trim_antarctica=False, flesh_out_antarctica=False, mark_antarctica=False,
-		filter_field=None, filter_values=None) -> str:
+		trim_antarctica=False, flesh_out_antarctica=False, fuse_russia=False,
+		mark_antarctica=False, filter_field=None, filter_values=None) -> str:
 	result = ""
 	for shape, record in load_shaperecords(filename):
 		if filter_field is not None:
@@ -27,7 +27,7 @@ def plot_shapes(
 		is_antarctica = shape.points[0][1] < -60
 		if is_antarctica:
 			if trim_antarctica:
-				shape.points = trim_edges(shape.points, shape.parts)
+				shape.points, shape.parts = trim_edges(shape.points, shape.parts)
 			elif flesh_out_antarctica:
 				shape.points = lengthen_edges(shape.points)
 			if mark_antarctica:
@@ -35,6 +35,8 @@ def plot_shapes(
 					clazz_for_this_section = "antarctic"
 				elif "antarctic" not in clazz_for_this_section:
 					clazz_for_this_section += " antarctic"
+		if fuse_russia:
+			shape.points, shape.parts = fuse_edges(shape.points, shape.parts)
 
 		result += plot(shape.points, midx=shape.parts, close=False,
 		               clazz=clazz_for_this_section, fourmat='xd')

src/zupplemental/helpers.py

@@ -4,7 +4,8 @@ import random as rng
 from typing import Any, Iterable, Optional
 
 import shapefile
-from numpy import pi, sin, cos, tan, arcsin, arccos, degrees, ceil, radians, arctan2, hypot
+from matplotlib import pyplot as plt
+from numpy import pi, sin, cos, tan, arcsin, arccos, degrees, ceil, radians, arctan2, hypot, cumsum, transpose
 
 
 def load_shaperecords(filename) -> Iterable[ShapeRecord]:
@@ -125,15 +126,67 @@ def plot(coords: list[tuple[float, float]], midx: Optional[list[int]] = None, cl
 def trim_edges(coast, coast_parts):
 	"""remove the extra points placed along the edges of the Plate Carree map"""
 	for i in range(len(coast)-1, -1, -1):
+		if i in coast_parts:
+			continue
 		x0, y0 = coast[i-1] if i > 0 else coast[i]
 		x1, y1 = coast[i]
 		x2, y2 = coast[i+1] if i < len(coast)-1 else coast[i]
-		if (i not in coast_parts) and (abs(x0) > 179.99 or abs(y0) > 89.99) and (abs(x1) > 179.99 or abs(y1) > 89.99) and (abs(x2) > 179.99 or abs(y2) > 89.99):
+		if (abs(x0) > 179.99 or abs(y0) > 89.99) and \
+			(abs(x1) > 179.99 or abs(y1) > 89.99) and \
+			(abs(x2) > 179.99 or abs(y2) > 89.99):
 			coast.pop(i)
 			for j in range(len(coast_parts)):
 				if coast_parts[j] > i:
 					coast_parts[j] -= 1
-	return coast
+	return coast, coast_parts
+
+
+def fuse_edges(points: list[tuple[float, float]], part_indices: list[int]) -> tuple[list[tuple[float, float]], list[int]]:
+	"""look for parts with matching vertices on either side of the antimeridian and combine them"""
+	# first, we must apply the trimming algorithm.
+	points, parts = trim_edges(points, part_indices)
+	# break the data up into the individual parts
+	parts = []
+	for i in range(len(part_indices)):
+		start = part_indices[i]
+		end = part_indices[i + 1] if i + 1 < len(part_indices) else len(points)
+		parts.append(points[start:end])
+		if points[start] == points[end - 1]:
+			parts[-1] = parts[-1][:-1]  # also remove the duplicate endpoint
+
+	# look for pairs of parts with matching antimeridianal points, and stitch them together
+	parts = fuse_edges_of_parts(parts)
+
+	# put it all back into a single list of points and a list of moveto indices
+	for part in parts:
+		part.append(part[0])  # don't forget to undo the part where we removed the duplicate endpoint
+	points = sum(parts, start=[])
+	part_indices = cumsum([len(part) for part in parts])
+	part_indices = [0] + list(part_indices[:-1])
+	return points, part_indices
+
+
+def fuse_edges_of_parts(parts: list[list[tuple[float, float]]]) -> list[list[tuple[float, float]]]:
+	"""look for parts with matching vertices on either side of the antimeridian and combine them"""
+	for i in range(len(parts)):
+		# look at every point in part i
+		for j in range(0, len(parts[i])):
+			# search for any that are on the antimeridian, and after another on the antimeridian
+			if abs(parts[i][j][0]) > 179.99 and abs(parts[i][j - 1][0]) > 179.99:
+				for k in range(i):
+					# look at every point in part k
+					for l in range(len(parts[k])):
+						# search for any that are on the antimeridian, and after another on the antimeridian
+						if abs(parts[k][l][0]) > 179.99 and abs(parts[k][l - 1][0]) > 179.99:
+							# if the two points' latitudes match
+							if abs(parts[i][j - 1][1] - parts[k][l][1]) < 0.01:
+								# do the stitching
+								parts[i] = parts[i][:j] + parts[k][l:] + parts[k][:l] + parts[i][j:]
+								parts.pop(k)
+								# recurse in case we need to stitch together a few in a row
+								return fuse_edges_of_parts(parts)
+	# return the unmodified list if we found absolutely noting to fuse
+	return parts
 
 
 def lengthen_edges(coast):