Topognosia: how many competitors are around an address
Area and business analysis from open data.
The problem
Anyone thinking of opening a business asks how many others already do the same nearby. The data exists in the Greek business registry, but not in a form that answers that question by area.
What I built
- Collection from the GEMI registry within its API rate limit, joined with the census and municipal boundaries
- Address geocoding and a business counter on a hexagon map grid
- "Where is it missing?": the municipalities with the fewest businesses of a sector per 1,000 residents
- A 0–100 activity index and side-by-side municipality comparison
- Sole proprietorships and small partnerships are never named or placed on the map
What it covers today
- Active businesses
- 1,046,197
- Municipalities published
- 332
- Registry data
- 01–02/10/2026
Figures as of 19/10/2026, taken from the site itself.
Technology
Astro, Cloudflare D1, Cloudflare R2, PostGIS, Nominatim, H3, PMTiles