Determining which other geographies a given geography shares borders with using geojson

Question

Is it possible using either topojson or geojson to determine which features (i.e. countries, states, municipalities) a given feature shares borders with? For those unfamiliar with geojson, the data structure looks like the following:

{
  "type": "FeatureCollection",
  "features": [
     {
       "type": "Feature",
       "id": "01",
       "properties": { "name": "Alabama" },
       "geometry": {
         "type": "Polygon",
         "coordinates": [[[-87.359296,35.00118],
           [-85.606675,34.984749],[-85.431413,34.124869],
           [-85.184951,32.859696],[-85.069935,32.580372],
           [-84.960397,32.421541],[-85.004212,32.322956],
           [-84.889196,32.262709],[-85.058981,32.13674] …
          ]]
      }
    },
    {
         "type": "Feature",
         "id": "02",
         "properties": { "name": "Alaska" },
         "geometry": {
           "type": "MultiPolygon",
           "coordinates": [[[[-131.602021,55.117982],
             [-131.569159,55.28229],[-131.355558,55.183705],
             [-131.38842,55.01392],[-131.645836,55.035827],
             [-131.602021,55.117982]]],[[[-131.832052,55.42469],
             [-131.645836,55.304197],[-131.749898,55.128935],
             [-131.832052,55.189182], …
            ]]]
          }
      }
// ... more features ...
}

Answer 1

The problem here is independent of format, but TopoJSON makes this very easy - there's actually a library method topojson.neighbors(objects), which should offer exactly what you need:

Returns an array representing the set of neighboring objects for each object in the specified objects array. The returned array has the same number of elements as the input array; each element i in the returned array is the array of indexes for neighbors of object i in the input array. For example, if the specified objects array contains the features foo and bar, and these features are neighbors, the returned array will be [​1, [0]​], indicating that foo is a neighbor of bar and vice versa.

Answer 2

The GeoScript library has a Javascript (also Python, Groovy & Scala) implementation. This library contains the geom.Geometry class which has a method called Geometry.touches which can test if one geometry touches another geometry. That's exactly what you need.