Add --svg-layers option for plotter-friendly SVG output with layers sorted by line size

[iret33]

Summary

Adds a new --svg-layers CLI flag that creates plotter-friendly SVG output with roads organized into separate layers by line width. This is ideal for:

• Pen plotters (AxiDraw, etc.) - plot each road type with different pen sizes
• Laser cutters - separate passes for different line weights
• Vector editing (Illustrator, Inkscape) - easily select/modify road categories

Road Layers (sorted by line size)

Layer	Road Types	Line Width
Residential & Other	residential, footway, paths	0.4
Tertiary Roads	tertiary	0.6
Secondary Roads	secondary	0.8
Primary Roads	trunk, primary	1.0
Motorways	motorway	1.2

Each layer has an identifiable gid attribute in the SVG for easy selection.

Usage

# Generate plotter-friendly SVG with separate layers
python create_map_poster.py -c "Berlin" -C "Germany" -f svg --svg-layers -d 10000

Example Output Files

Sample SVG files included in this PR (see examples/svg-layers/):

• manama_bahrain.svg - Manama, Bahrain
• dubai_uae.svg - Dubai, UAE
• cairo_egypt.svg - Cairo, Egypt

All files contain 5 properly separated SVG layers:

grep -o 'id="layer_[^"]*"' examples/svg-layers/manama_bahrain.svg
# id="layer_residential_Residential_&_Other_width_0.4"
# id="layer_tertiary_Tertiary_Roads_width_0.6"
# id="layer_secondary_Secondary_Roads_width_0.8"
# id="layer_primary_Primary_Roads_width_1.0"
# id="layer_motorway_Motorways_width_1.2"

Additional Tested Cities

Bahrain (Top 5 Cities):

• Manama, Muharraq, Riffa, Hamad Town, Isa Town

Top 5 Arab Cities:

• Cairo (Egypt), Riyadh (Saudi Arabia), Dubai (UAE), Baghdad (Iraq), Jeddah (Saudi Arabia)

Use Cases

Pen Plotter Workflow

1. Generate SVG with --svg-layers
2. Open in Inkscape
3. Plot residential roads with 0.3mm pen
4. Swap to 0.5mm pen, plot primary roads
5. Swap to 0.8mm pen, plot motorways

Laser Cutter Workflow

1. Generate layered SVG
2. Assign different power/speed settings per layer
3. Cut with varying line depths

Test Plan

• Generate SVG without --svg-layers (standard behavior unchanged)
• Generate SVG with --svg-layers and verify layers appear as separate groups
• Verify layer IDs present in SVG output
• Tested with 10 different cities across multiple countries
• PNG/PDF output unaffected by the new flag

🤖 Generated with Claude Code

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved.

[merwok]

(Could the github action be configured to edit labels but not add comments?)

[iret33]

That's a question for the repo maintainer (@originalankur) - the conflict-checking workflow is configured on the upstream repository, not on my fork.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved.