Wednesday, June 27, 2018

What About Vector Tiles in GeoPackage?

I periodically get questions about whether GeoPackage can/will/should support vector tiles. Without getting into the benefits or drawbacks of vector tiles, let's just say it is an emerging capability that is getting a lot of community interest. As it turns out, supporting vector tiles in GeoPackage is the easy part. We already have a precedent for handling types other than features and raster tiles - the tiled gridded coverage extension.

The real issue is that OGC has not yet adopted an approach for vector tiling. What is the content encoding for a vector tile? Is it Protocol Buffers (as per Mapbox Vector Tiles - MVT)? GeoJSON? Something else? OGC members are reluctant to support a vector tiling approach that is only used with GeoPackage. (Supporting one-off solutions often has a poor cost-benefit story.) OGC simply needs to make a decision and a community standard would suffice.

Once OGC makes a decision, it is a straightforward matter to support it in GeoPackage. We would create a new extension that would define a new content type that depends on the tiles option. I don't think there would be any other ancillary tables like were needed for tiled gridded coverages, but if there are we can add those. This would get us to a community extension which will satisfy some people. If we want an official (OGC adopted) extension then we have to go through the normal process of OAB approval, open comment period, TC vote, etc. This process will probably go smoothly as long as we have proof of implementation.

UPDATE: After talking with a few people, I went ahead and drafted a community extension based on the MVT approach.

UPDATE #2: In response to this issue, OGC initiated the Vector Tiles Pilot.

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