mojodna/mapshaper-proxy

mapshaper-proxy

This is an HTTP proxy for MapShaper. It allows tiled JSON sources to be processed on the fly by providing MapShaper commands in the URL.

Starting

SOURCE=http://localhost:8000/{z}/{x}/{y}{scale}.json npm start

Requesting Tiles

This is a URL template (suitable for handing to Tangram or other tools that consume tiled GeoJSON) that will filter out small features, clean up gaps, and simplify. It will also pass ?sieve=12 to the underlying tile source.

http://localhost:8080/{z}/{x}/{y}.json?cmds=-filter%20%22this.originalArea%20%3E%20%7B%7Bmath%20resolution%20%22*%22%201000%7D%7D%22%20-clean%20min-gap-area%3D%7B%7Bmath%20resolution%20%22*%22%2065000%7D%7D%20-simplify%20interval%3D%7B%7Bmath%20resolution%20%22*%22%202%7D%7D&sieve=12

To break this down, there are 2 query parameters included: cmds and sieve. cmds is the only parameter that mapshaper-proxy cares about; all others will be passed to the underlying tile source.

cmds is a set of URL-encoded MapShaper commands. In this case, it's:

-filter "this.originalArea > {{math resolution "*" 1000}}"
-clean min-gap-area={{math resolution "*" 65000}}
-simplify interval={{math resolution "*" 2}}

(Decoded using decodeURIComponent() in a JavaScript console. Newlines were added by hand.)

Commands may include handlebars expressions to facilitate dynamic functionality. At present, resolution and zoom are made available as variables to the template. Because handlebars does not natively support math expressions, a custom math handler is included, explaining the funky syntax.

To create your own cmds query parameter, run encodeURIComponent("-simplify 20%") (or similar) in a JavaScript console to encode it.