[GIS] Create basemap tiles for a custom shape (for reducing the tiles count)

tilemilltiles

in order to create a world wide tiles (for a basemap) in acceaptable zoom level one must have a huge hd (see in this post). but, most of the world is sea…

so i want to create x levels of the whole world (x is small say 5-10) and then y levels of only the mainland (y is big say 20) and by that save allot of cpu time for the tile creatiion and hd space for saving unneeded tiles.

i use tilemill to create tiles and you can only define a bounding box rectangle.

can anyone recommend a solution (or maybe a different approach?)

thanks!

edit:
the tiles are created from osm data

Best Answer

For lower zoom levels, I decided to take the NASA Blue Marble as tile source.

The original is downloadable here: http://visibleearth.nasa.gov/view.php?id=57752

For zoom levels 0 to 4, I took the small one and made the tiles with gdal2tiles:

gdal2tiles --s_srs EPSG:4326 --zoom 0-4 D:\Karten\Geotiff\BlueMarble\bluemarble.tif D:\Tiles\test

Fro zoom level 5 to 7, I took the high-resolution of half the world:

gdal2tiles --s_srs EPSG:4326 --zoom 5-7 D:\Karten\Geotiff\BlueMarble\bluemarble-ost.tif D:\Tiles\test

Gdal2tiles needs a little patch to use the OSM-like tile naming. I described the workflow here: GDAL2Tiles: MapTiles from BSB/KAP are Switched

You only have to do that once, as the world does not change much looking at low zoom levels.

My OSM tiles built with Mapnik start at zoom level 8. This can be defined in generate_tiles.py

To save disk space, I wrote a little recursive batch file to delete empty tiles:

for /R .\ %%N IN (*.PNG) DO if %%~zN LSS 120 del %%N

This works for Windows, you have to test which file size in bytes is best for you.

EDIT

Another choice is to set up a bunch of bounding boxes covering the coastlines in a better way than one single bounding box does. This will save creation time as well.

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