Joining data against PLUTO

join.js

// New York City PLUTO shapefiles are pretty big.
// If you have data by BBL and want to join it
// against PLUTO shapes but you don't like QGIS
// or PostGIS, you could convert it to GeoJSON
// `ogr2ogr -f "GeoJSON -t_srs "EPSG:4326" pluto.geojson pluto.shp`
// And then stream it like this.

var fs = require("fs"),
    _ = require("underscore"),
    through = require("through"),
    JSONStream = require("JSONStream");

// Our list to join
var dataByBBL = {
  "1234567890": {
    some: "data",
    more: "data"
  },
  "1231231231": {
    some: "data",
    more: "data"
  },
  "4564564564": {
    some: "data",
    more: "data"
  }
};

// Stream PLUTO, one feature at a time
fs.createReadStream("pluto.geojson",{encoding:"utf8"})
  .pipe(JSONStream.parse("features.*"))
  .pipe(through(function write(feature){

    // Ignore this lot, we don't care about it
    if (!dataByBBL[feature.properties.BBL]) {
      return true;
    }

    // Stream the feature with our data added to the properties
    this.queue(_.extend(feature,dataByBBL[feature.properties.BBL]));

  }))
  .pipe(JSONStream.stringify(
    '{"type": "FeatureCollection", "features": [', //opening string
    ",", //separator between features
    "]}" //closing string
  )) // Write back out to GeoJSON
  .pipe(fs.createWriteStream("joined-with-pluto.geojson"));