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I have downloaded the OSM file for Sydney and imported it into QGIS. As you can see I have all the lines and areas. However, there is no polygon for the land itself, and no polygon for the neighbouring Pacific ocean, and no polygon for the water in the Sydney harbour, which then snakes inland into the Parramatta river. I thought these would be very large polygons, and that's why they don't show up - they are larger than the bounding box of Sydney. However, I tried downloading the OSM for New South Wales but I still don't have the land mass, oceans, or rivers. I then thought maybe those polygons are special and need to be generated - I found http://openstreetmapdata.com/data which has land and water polygons. That gives me the land, the sea, but not the water polygon for the Sydney harbour and the main Parramatta river. What am I doing wrong?
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In OpenStreetMap the land and the sea/ocean aren't explicitly mapped. Instead the coastline is mapped as a way (line) https://wiki.openstreetmap.org/wiki/Coastline. From the coastline, you can generate polygons for the land and/or ocean. https://wiki.openstreetmap.org/wiki/OSMCoastline is one such tool which does this as you've found out. Sydney Harbour https://www.openstreetmap.org/relation/1252425/history has seen some recent edits, so you might need to re-download your data, but it should show up since it's tagged as a multipolygon. |
