Vector tile analysis

[yhahn]

@kkaefer has been pining for some stats regarding our vector tiles. I'm guessing he's interested in maxes but some kind of median/average value would be useful as well.

• Determine sample size/method -- e.g. grab tiles from major cities, minor cities, across several zoom levels ?
• Decide on necessary analyses (number of features, number of coordinates per feature, etc.)
• Build out basic script to fetch and run analysis

Guessing even without strong decisions around these we can adjust as it becomes clearer what kind of info is necessary.

• node-mapnik and how to convert VT to json easily for analysis https://github.com/mapnik/node-mapnik/blob/master/test/vector-tile.test.js#L128-L135
• fixture data for locations/bboxes of various cities https://github.com/mapbox/generate-geo-testing-data/blob/master/data/cities.json
• grab the vector tiles based on http://a.tiles.mapbox.com/v3/mapbox.mapbox-streets-v3.json

[kkaefer]

• for every layer, the number of features on the layer, and the number of vertices per feature (and the overall number of vertices of that layer)
• for every feature, the total line/perimeter length
• number of vertices that are outside the extent range (typically from 0..4096 on both axes)
• something like taginfo for our vectortiles, that shows the typical tags/values per layer
• for all of these metrics, average and median, and min/max overall and per zoom level

[kkaefer]

oh, and byte size for feature/layer would be interesting too. you can only compute this on a protobuf level, not with the mapnik/tojson functionality

[dmitrig01]

See statistics branch.

• run node index.js to get a list of cities
• run node index.js [cityNumber] [5≤zoomLevel≤17] to get statistics for that city at that zoom level.

[dmitrig01]

Oh, make a directory tilecache