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Geometry mapping antipattern: landuse=snake

Posted Thu Dec 22 15:40:41 2022 Florian Lohoff

No. 2 of my antipatterns: "Landuse drag". Mappers seem to have the tendency to make little small pieces into one large, huge, even gigantic object. So they start dragging the landuse (and other objects) further and further along a road, across a road or whatever. The resulting object then rather looks like a very long snake following some arbitrary other object.

These snake like objects, or huge objects have the tendency to break pretty regular. More complexity is a unavoidable consequence by suddenly you are in the need of multipolygon relations, or unexperienced mappers accidentally break the object.

So - With landuse its like with all others things in life - Keep it simple and stupid.

See this example where someone tried to include the 4 trees on the other side of the road into the MUCH larger forest area. The falsely included area of the streets outweights by far the correctly included area. The other problem is that the boundaries of the landuse now do not follow visible contrast in the aerial imagery. Very confusing.

Another example is this. Landuse is beeing dragged along a street, making the landuse=residential a backdrop of the street. It includes the full streets width although only one side really contains residential usage. The south-east part should really be its own landuse stopping at the shoulder of the street. Again the abuse of landuse to try to make a "gapless" map makes these geometries a lot more complex than they need to be.

The last example for today is this. Dragging the landuse across a huge intersection, just to include the 4 other building on the other side. This includes more area used for traffic than it includes real residential area. Again the perimeter of the landuse does not follow any visible contrast boundary in the aerial imagery, crossing the roads in absurd and completely random angles.

So to summarize: Landuses should follow stuff you can actually see in an aerial. They should not erratically cross other objects or include other objects/area which are not represented by this landuse. Landuses are not a "backdrop" behind streets just to make the map "gapless".

If it gets to complicated, split it into smaller chunks.