OSMnx · Clean up the graph
Project to a metric CRS, convert between graph representations, consolidate intersections, trim to a study area. Mirrors the Graph Operations panel.
Needs an active downloaded network (Download a street network).
1. Project to a metric CRS
Fresh downloads are in degrees. Project Graph reprojects to a local UTM zone so lengths and areas come out in meters. Do this before anything that measures distance.
2. Convert representations
To Undirected collapses two-way streets into single edges, which orientation statistics require. To DiGraph gives a simple directed graph keyed by length. Graph → GDFs and GDFs → Graph round-trip through GeoDataFrames for external editing.
3. Consolidate intersections
Complex junctions are often modeled as several nearby nodes. Tolerance (default 10 m) sets how close nodes have to be to merge into one. Worth doing before centrality analysis.
4. Truncate to a study area
Truncate by Distance works in network distance from a source node, not straight-line distance. Truncate by BBox and Truncate by Polygon clip to a rectangle or a polygon object.
5. Keep the largest component
Largest Component drops disconnected fragments and leaves one contiguous network.
Next steps
Add edge attributes: lengths, speeds, travel times.