OpenStreetMap Data in Layered GIS Format // Version 0.7.11
2.7 Layers
In OSM there are no layers in the traditional GIS sense. All features are in one big coherent
database.
For the purpose of the mapping described in this document, the features stored in the OSM
database are extracted into dierent layers depending on their type.
All layers dened in this document use the “osm_” prex for their names.
To allow for future changes of this document, the document version number is embedded in
the layer names. So the “roads” layer in version 1.0 is called “osm_roads_v10” in le names,
WMS layers etc.
2.8 Points and Areas
e availability of high-resolution aerial imagery has led to many POI features being
recorded as areas (building or site outlines), not points, in OpenStreetMap. You will, for
example, oen nd a restaurant or hotel drawn as an area. is makes processing dicult
because you have to cater for both types of POIs even if you are not interested in areas.
e Geofabrik shape les alleviate this problem by converting any area feature to a point,
and adding it to the appropriate point layer. All point layers which are marked as having an
“associated area layer” in this document work this way. ey will have an extra “geomtype”
column that has one of the three values “N” (=the feature stems from a node, or point, in
OSM), “W” (=the feature stems from a way, a simple area, in OSM), or “R” (=the feature
stems from a multipolygon relation in OSM). For these layers, there will be an extra shape
le with the name sux “_a” containing the proper polygon.
So in case you are not interested in areas, you can just ignore the “geomtype” column in the
point shape, and process everything normally. e automatic conversion of areas to points
will make sure that you do not lose any information. If, however, you would like to process
areas wherever they are available, then you should disregard the auto-converted objects of
types “W” and “R” from the point shape, and additionally use the polygons from the _a
shape.
Note that sometimes features are contained twice in the OSM database, once as point and
once as area. If this happens, they will turn up twice in these layers.
2.9 Spillover Shape Files
When a certain layer becomes too large for one shape le (shape les are limited to 2 GB in
size), it will automatically spill over into additional shape les. A shape le named
“osm_pois_v07_1.shp” will have spillover shape les names “osm_pois_v07_2.shp”,
“osm_pois_v07_3.shp” and so on.
6
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