TopoJSON (Topology-Aware JSON)
Open BetaTopoJSON è un'estensione di GeoJSON consapevole della topologia. Usa la codifica ad archi condivisi (i confini tra poligoni vengono memorizzati una sola volta) e la quantizzazione intera delle coordinate: il file risultante è del 60-80% più piccolo di un GeoJSON equivalente. Input standard per D3.js, Mapshaper e Observable; ideale per mappe coropletiche interattive e atlanti web.
Caratteristiche principali
Informazioni sul formato TopoJSON
TopoJSON was invented by Mike Bostock, the author of D3.js, to solve a simple problem: in GeoJSON neighboring polygons store their shared border twice. TopoJSON moves all the lines into a common array of arcs that the objects then refer to. On top of that, coordinates are rounded to an integer grid and written as increments — the file gets sharply lighter.
The format is taken for web graphics and analytics: choropleths in D3, interactive atlases, boundary maps in Observable, lightweight layers for offline applications. The second motive is simplification: during generalization the shared borders move together, and no gaps appear between neighboring districts.
The output is a single document: every layer becomes a separate object inside it — roads, buildings, water and so on — and object attributes are preserved. Coordinates are in WGS84, up to 100,000 objects per layer. The topology is built by our own code, with no external dependencies.
The price of compactness is the rounding of coordinates. The grid step depends on the size of the area: for a district it is on the order of a meter, for a country hundreds of meters. For a web map that is invisible; for precise measurements take GeoJSON or GeoPackage.
Quale programma apre i file TopoJSON
I seguenti programmi e applicazioni possono aprire, modificare ed elaborare i file TopoJSON (Topology-Aware JSON) (.topojson) esportati da OSM2CDR:
Format specifications
- Open standard
- 2D only
- Lossless (no quality loss)
- Stores feature attributes
- Output: 1 file
- TopoJSON (open spec). Topologically encoded GeoJSON: shared borders stored once, file size 30-80% smaller. Used by D3.js.
Chi usa le mappe TopoJSON
Come esportare in TopoJSON
Come aprire il file dopo l'esportazione
- D3.js — include topojson-client and unpack the layer you need: topojson.feature(topology, topology.objects.buildings), then the usual d3.geoPath.
- Mapshaper — drag the file onto mapshaper.org: objects and attributes are visible, and simplification and export to SHP or GeoJSON are right there.
- QGIS — opens .topojson as an ordinary vector layer through GDAL; handy for checking the geometry with your own eyes.
- Converting to GeoJSON — topo2geo buildings=buildings.geojson < map.topojson from the topojson-client package, or ogr2ogr.
- Leaflet and MapLibre — they do not understand the format directly: unpack it into GeoJSON on the client with the topojson-client library and feed it on as usual.
Mappe popolari in TopoJSON
Ottieni esportazioni di mappe in TopoJSON (Topology-Aware JSON)
Scarica mappe TopoJSON professionali da OpenStreetMap. Generazione istantanea, qualsiasi area.