mad-science@ricepo

This package can compute isodistance polygons based on driving distance.

Getting Started

$ git clone git@github.com:ricepo/isodist.git
$ cd isodist
$ npm install

In order to run isodist, you will need to download an *.osm file corresponding to the region where you want to do your computation. Geofabrik is a good source of these files.

You need to place your OSM files into the isodist/osrm directory (create one if it does not exist). Then run the following command to generate .osrm files:

$ npm run prepare

Finally, you are good to go! In order to generate the graph above, you will need indiana.osrm and run the following:

$ isodist --lon=-86.893386 --lat=40.417202 -s 2 -s 5 -s 7 -r 0.1 -h 0.5 -m indiana

Input file

You can specify all the parameters in an input file that is piped into standard input:

/* input.json */
{
  "origin": {
    "type": "Point",
    "coordinates": [ -86.893386, 40.417202 ]
  },
  "map": "indiana",
  "steps": [{
      "distance": 2
  }, {
      "distance": 5
  }, {
      "distance": 7
  }]
}

$ isodist < input.json

Please note that CLI arguments always override values specified in the input file.

$ isodist --map il < input.json
# The above command will use `osrm/il.osrm`

Command Line Arguments

--lat

Required.

Latitude of the origin point.

--lon

Required.

Longitude of the origin point.

-s, --step

Required.

Distance at which to compute isodistance polygons. For example, to compute isodistance polygons at 1, 2, 5 and 10 miles, use --step 1 --step 2 --step 5 --step 10

-m, --map

Required.

Name of the .osrm file you wish to use for routing.

-r, --resolution

Optional, default: 0.2

Sampling resolution of the underlying point grid. Larger values will result in less precise results but much faster processing. Smaller values will produce more precise results, but will require exponentially more processing time and memory.

Having a very small resolution value may result in kinks (i.e. self-intersections) of isodistance polygons, which cause hex-fitting to fail. You can choose to ignore them by disabling hex-fitting, but note that presence of kinks usually indicates incorrect parameter choice.

-h, --hex-size

Optional, default: 0.5

Size of hex grid cells that isodistances are fitted onto. Passing a 0 value will disable hex grid fitting.

--no-deburr

Optional, default: none

This flag instructs isodist not to remove isolated "islands" from isodistance geometries.