TopoJSON (Topology-Aware JSON)
Open BetaTopoJSON ir topoloģiju atbalstošs GeoJSON paplašinājums. Izmanto koplietotu loku kodēšanu (robežas starp daudzstūriem tiek glabātas tikai vienreiz) un koordinātu veselo skaitļu kvantēšanu — iegūtais fails ir par 60–80% mazāks nekā līdzvērtīgs GeoJSON. Standarta ievaddati programmām D3.js, Mapshaper un Observable; ideāli piemērots interaktīvām horoplētkartēm un tīmekļa atlantiem.
Galvenās iespējas
Par TopoJSON formātu
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.
Kura programma atver TopoJSON failus
Tālāk norādītās programmas un lietotnes var atvērt, rediģēt un strādāt ar TopoJSON (Topology-Aware JSON) (.topojson) failiem, kas eksportēti no 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.
Kas izmanto TopoJSON kartes
Kā eksportēt TopoJSON
Kā atvērt pēc eksporta
- 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.
Populāras kartes formātā TopoJSON
Eksportējiet kartes formātā TopoJSON (Topology-Aware JSON)
Lejupielādējiet profesionālas TopoJSON kartes no OpenStreetMap. Tūlītēja ģenerēšana, jebkurš apgabals.
Biežāk uzdotie jautājumi
Convert to TopoJSON and back
What people who already downloaded say
Reviews are quoted in the language their authors wrote them in.
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