geoArea should (?) also work with a list of coordinates about d3-polygon HOT 3 CLOSED

Are you confusing d3.geoArea from d3-geo with d3.polygonArea from this repository, d3-polygon?

d3.geoArea takes a GeoJSON object as input, and assumes it is in spherical coordinates (x = longitude and y = latitude in degrees). It computes the spherical area the GeoJSON object.

path.area also takes a GeoJSON object as input, but you can use path.projection to project the GeoJSON object before computing its planar area. Most commonly this is used to project spherical geometry to planar geometry, but if the projection is null or a d3.geoIdentity instance, you can pass planar geometry to path.area and it will compute the (possibly transformed) planar area.

Lastly d3.polygonArea only accepts an array of coordinates representing a ring as input. (This common definition of a polygon is simpler than the one GeoJSON uses, as the GeoJSON definition allows polygons to have holes.)

If you have a spherical GeoJSON MultiPolygon geometry object and you want to compute the spherical area of a constituent polygon, you’ll need to do something like this:

// Given a MultiPolygon GeoJSON geometry object…
var multiPolygon = {type: "MultiPolygon", coordinates: […]};

// Construct a Polygon GeoJSON geometry object from the multipolygon.
var polygon0 = {type: "Polygon", coordinates: multiPolygon.coordinates[0]};

// Compute the spherical area of that polygon.
var area = d3.geoArea(polygon0);

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Thank you! 🤗

from d3-polygon.

Thank you for untangling the d3.geoArea, path.area and d3.polygonArea functions. I may have opened this issue at the wrong location.

But I was not looking for help :) I was just suggesting that d3.geoArea too could work directly with a list of coordinates. (Although I also get your point that it's not that difficult to work around, it took me quite a while to figure out how to do it.)

from d3-polygon.

d3.geoArea takes a GeoJSON object. An array of coordinates is not a GeoJSON object, and it would be difficult to infer what type of geometry an array of coordinates represents (ring, polygon, multipolygon, etc.). That’s kind of the point of GeoJSON: to tell you what an array of coordinates represents.

from d3-polygon.