One task where GeoJSON falls down is simplification of a group of polygons with common boundaries, e.g. the 48 conterminous US states. If you start with a highly detailed set of polygons, you need to simplify them for practical display in an online map.

GeoJSON doesn't encode the fact that the boundary points are common between adjacent polygons. When you simplify those polygons, each one is handled separately, and you end up with "slivers" where the boundaries are misaligned:

https://www.bing.com/images/search?q=map+slivers+betwen+poly...

TopoJSON solves this by encoding each such boundary only once. So when you simplify the polygons, they are all done together, and the same simplification applies to adjacent polygons. No more slivers!

https://github.com/topojson/topojson

https://github.com/topojson/topojson-simplify

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Demiurge 3 hours ago | parent | next [-]

Is this actually GeoJSON falling down, or decades of convention extended to JSON? Topology is great, but it is sidestepped by Shapefile/WKT/WKB/etc, in favor of independent primitives like POINT, LINE, POLYGON. If GeoJSON did not exist as a new JSON GIS data format encoding these primitives, TopoJSON would not have "replaced" it, due to the added mis-match with other non-topological formats.

From what I can tell, the top criticism of GeoJSON is the under-enforced winding order specification, and crossing the antemeridian.

	▲	jvanderbot 3 hours ago \| parent [-]
		Right. Encoding a union algorithm into the data structure just introduces the reverse problem: Selecting a subset now requires extra logic beyond jq.

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pramsey an hour ago | parent | prev | next [-]

GeoJSON is not TopoJSON. Saying that is "falling down" is like criticizing a zebra for not being a giraffe. GeoJSON is a mapping of the (non-topological) "simple features" model into JSON, full stop. It does that fine.

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echoangle 2 hours ago | parent | prev [-]

How is that a geojson problem? If your dataset is correct, adjacent borders will just use the same points and will match exactly.

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sdenton4 2 hours ago | parent [-]

The problem is simplification. Suppose two regions share a border with some nonlinear points a, b, c, d. Simplifying the polygon for the first region might yield a, b, d while the second yield a, c, d. This creates gaps or overlaps between the two regions.

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echoangle 2 minutes ago | parent | next [-]

So don’t simplify the shapes on their own. Geojson is a storage and exchange format, you can still convert it to other formats if you want to modify it.

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qurren 10 minutes ago | parent | prev [-]

But what is the border? Set the border to what it actually is, not a simplification of it. The state of Colorado is formally a 697 sided polygon, don't simplify it to a rectangle.

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tomrod 6 minutes ago | parent [-]

This is not what OP is describing. It is very common to simplify objects for decreasing boundary objects by orders of magnitude. GeoJSON is missing correlation when you do that. Simplifying country objects from a GeoJSON source could lead to a gap between the country borders. So you either have poor representation or a longer pipeline to convert objects to an amenable object set. It also breaks idempotency in some regards.

	▲	echoangle a few seconds ago \| parent [-]
		To do the simplification, you detect shared borders, simplify and generate polygons again. That doesn’t make topojson inherently superior. You can convert back and forth and for many applications geojson is easier to process.