[OSM-dev] Vector tile based raster rendering - toolchain architecture

[Nelson Minar]

I just wanted to add my excitement for the growth of vector tile work with
OpenStreetMap. Most of the mapping industry is moving to vector tiles; the
big mobile maps apps like Google's and Apple's are vector based, as are
many newer browser maps like the Google Maps redesign. Offline maps also
benefit greatly from vector maps, such as Skobbler's ForeverMap apps. Part
of the reason to use vector maps is because the amount of data is smaller,
also because client-side rendering has gotten fast enough that it can do
nicer rendering than a static raster from the server (particularly with
WebGL).

There are a couple of experimental OSM vector tile servers that are working
today. I don't know if these provide ideas for server architecture, but
they are useful if you want to do client experiments.

Mike Migurski's is here:
http://openstreetmap.us/~migurski/vector-datasource/
Mapzen's is here:
https://github.com/mapzen/vector-datasource/wiki/Mapzen-Vector-Tile-Service


As for vector format, I gave a talk at SotM US 2013 on TopoJSON that
includes some measurements of data sizes. Slides and video linked here:
http://www.somebits.com/weblog/tech/topojson-sotm-us-2013-talk.html

GeoJSON is the obvious choice but it's a pretty inefficient encoding.
Delta-encoding line segments, so coordinates are relative instead of
absolute, makes for an enormous space savings. That's the main reason for
the space savings in TopoJSON I found. Also a binary encoding like Protocol
Buffers does make for a significantly smaller tile than the text encoding
of JSON. If I were designing a major new tile service now I'd look to
MapBox's vector tile format as a guide. Dane and crew have been working on
that format for a year+ and it looks pretty solid.
https://github.com/mapbox/mapnik-vector-tile
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