Merging Shapefiles with JavaScript

GeoScript aims to provide a framework for scripting common data processing tasks with GeoTools and the Java Topology Suite. Much in the same way that scripting languages like Python can leverage the powerful OGR/GDAL libraries, GeoScript offers similar functionality from languages that run on the JVM (currently Groovy, JavaScript, Python, or Scala).

In a recent post on his blog, Darren Cope wrote about merging a directory of shapefiles, a common data processing task. Here I'll demonstrate how to do the same thing with the JavaScript version of GeoScript.

This example uses the workspace and layer modules. I'm working with a directory containing shapefiles of US Census block groups for each state, merging them into a single shapefile for the country.

// import modules
var workspace = require("geoscript/workspace");
var layer = require("geoscript/layer");

// create workspaces from existing directories
var source = new workspace.Directory("path/to/source_dir");
var target = new workspace.Directory("path/to/target_dir");

// iterate through layers in source workspace
var country;
source.names.forEach(function(name) {
    // create state layer from existing shapefile
    var state = source.get(name);
    // create country layer first time through
    if (!country) {
        country = new layer.Layer({
            schema: state.schema.clone({name: "country"})
        });
        // this creates the new shapefile on disk
        target.add(country);
    }
    // iterate through source features to add each to target 
    state.features.forEach(function(feature) {
        country.add(feature);
    });
});

While it is hard to beat the terseness of the ogr2ogr example, the JavaScript version of GeoScript provides syntax that I hope is familiar to a larger population of scripters.