Using mapshaper programmatically

This page is for developers who want to use mapshaper's geoprocessing functions in their own Node applications. Updated for version 0.4.0

Option One: make

One way of scripting mapshaper is to call the mapshaper command line program from make or other build tool.

If you include mapshaper as a dependency in the package.json file of a Node.js project, the executable program can be found at this path: node_modules/.bin/mapshaper.

Here's an example Makefile target:

europe.json: shp/europe.shp
	mapshaper snap $< encoding=utf8  \
	-rename-layers countries \
	-filter "CONTINENT == 'Europe'" \
	-simplify 15% keep-shapes \
	-o format=topojson $@

Option Two: runCommands()

mapshaper.runCommands(commands, done)

• commands A command line string or an array of parsed command objects, starting with the -i command
• done A Node-style callback: function(Error)

// Example: converting a directory of Shapefiles to GeoJSON
var mapshaper = require('mapshaper');
mapshaper.runCommands('-i shapefiles/*.shp -o geojson/ format=geojson');

Option Three: applyCommands()

mapshaper.applyCommands(commands, input, done)

• commands A string containing command line arguments or an array of parsed commands.
• input JS object containing contents of files referenced by -i commands, indexed by file name.
• done A Node-style callback: function(Error, output). Output is a JS object containing the contents of generated files, indexed by file name.

applyCommands is similar to runCommands(), but it sends output to a callback instead of writing output files to the filesystem. The content of input files can be passed via the input parameter. Files not contained in the input object will be read from the filesystem.

// Example: converting a CSV string to GeoJSON
var csv = 'lat,lng,value\n40.3,-72.3,1000';
var cmd = '-i input.csv -points x=lng y=lat -o output.geojson';
mapshaper.applyCommands(cmd, {'input.csv': csv}, function(err, output) {
	var geojson = JSON.parse(output['output.geojson']);
});

Note on importing Shapefiles: To input a Shapefile using applyCommands(), in addition to passing the contents of the .shp file (as a Buffer or ArrayBuffer), you'll probably want to pass the .dbf file (as a Buffer or ArrayBuffer) and the .prj file (as a string). The .dbf file contains attribute data and the .prj file contains coordinate system data.