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tilelive-vector

Implements the tilelive API for rendering mapnik vector tiles to raster images.

Build Status

new Vector(options, callback)

  • xml: a Mapnik XML string that will be used to render vector tiles.
  • source: Optional, a uri string suitable for use with tilelive.load(). This is fallback source that will be used if no source is found as part of the Mapnik XML parameters.
  • base: Optional, basepath for Mapnik map. Defaults to __dirname.
  • format: Optional, target output format. Defaults to png8:m=h.
  • scale: Optional, Mapnik scale factor. Defaults to 1.
  • deflate: Optional, whether to expect deflated vector tiles. Defaults to true.
  • maxAge: Optional, length of time to hold vector tiles in memory cache. Defaults to 300e3 (300 seconds).
  • reap: Optional, time between reaps of vector tiles in memory cache. Defaults to 60e3 (60 seconds).

Code concepts

  • Backend z/x/y: a request for a raster tile at, say, 3/3/3 does not always mean 3/3/3 is requested from the backend source. The z/x/y requested from the backend source is referred in code by bz/bx/by and generally represent the same or lower zoom level. This allows for features like overzooming, maskLevel tiles, and scale factor adjustment.
  • Overzooming: if a tile beyond the maxzoom of the backend is requested, Vector will attempt to render the tile using the parent of the request at maxzoom.
  • maskLevel tiles: to avoid requiring many duplicate or empty vector tiles to be generated at high zoom levels, the backend source can specify a maskLevel. If a vector tile is not initially found at some z > maskLevel, Vector will issue an additional request to the backend using the parent tile of of the request at maskLevel. This allows a lower zoom level to "backfill" high zoom levels.
  • Scale factor adjustment: the scale argument decrements the backend zoom level such that the requested tile is the visual equivalent (when viewed on the proper dpi device) of its parent counterpart. For example, scale: 2 decrements bz by 1, scale: 4 decrements by 2, and so on.