The Drive-Time Trade Area
A retailer wants a 10-minute drive-time trade area around 250 stores. Street data is a local TomTom dataset; the spatial object is in WGS84 (lat/long). Analysts report that polygons look 'squashed' and that store points near the poles of a projected map fall outside their own polygons. Some stores sit within 50 m of a coastline and their polygons extend into water. The team also needs a count of competitor stores inside each trade area.
1. Diagnose the 'squashed' polygons and the points-outside-their-own-polygon symptom.
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Both symptoms point to a projection mismatch. Drive-time tools (e.g. Trade Area with a drive-time method) compute distances in a projected, distance-preserving CRS. If the input points are WGS84 lat/long and the tool or the spatial reference is not set consistently, distances are computed in degrees, which are not uniform, so polygons are distorted and points can fall outside their own areas.
Fix: project the store points to an appropriate projected CRS (e.g. a local State Plane or UTM zone) using the Spatial Info and Projection tools before building trade areas, and keep the street network in the same CRS. Verify with a Spatial Match that each store point falls within its own polygon; the count should equal the store count.
2. How should the coastal over-water problem be handled, and how should competitor counts be produced?
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Over-water polygons are a data/geometry issue, not a projection issue. Options: (a) clip trade areas to a land polygon layer with a Spatial Process (intersection) so water is removed, or (b) accept water but flag stores whose trade area is mostly water. Clipping is the defensible choice when the metric is 'population reachable', since water has no customers.
For competitor counts, use a Spatial Match (or Spatial Process 'Point in Polygon') between the competitor point layer and the trade-area polygons, then Summarize grouped by store to count matches. Ensure competitors and polygons share the same CRS before matching, and de-duplicate competitors that fall in overlapping trade areas if the business rule is 'unique competitors per store'.