[JT] Jochen Topf's Blog


Node Locations on Ways

OpenStreetMap has a somewhat peculiar data model. OSM ways don’t contain the locations of the points they go through, but only references to nodes, which in turn contain their location. This model has some advantages, but it also has a major disadvantage: For almost all uses of OSM, like drawing maps or calculating routes, the software has first to find the locations of all nodes in a way, before it can do anything with it. This is cumbersome and potentially expensive. To do this quickly, the lookup needs to be done in main memory without any disk access, but to store the locations of all nodes of a full planet file we already need about 32GB RAM. But maybe we can create a shortcut, so that we can do this once, instead of everybody doing this again and again?

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Tags: openstreetmap · osmium