Country Coder is a lightweight package that looks up region identifiers for geographic points without calling a server. It can code and convert between several common IDs:

In addition to identifiers, Country Coder can provide basic regional information:

This Is A Port

The original country coder and its data file was written by Quincy Morgan and Bryan Housel. See its documentaion for function reference and general description of what it can and cannot do.

Note that feature in function names here was replaced with region. For example, instead of featuresIn(), the CountryCoder class has regionsIn.

Also, geometries are not stored in RegionFeature objects that some of the methods return. This means, you get full information on a region, but not its boundaries.

Usage

You do not instantiate a CountryCoder, but use a static instance property. You should call load() once to initialize the instance. There is an option for asynchronous loading via prepareData() (see the API reference).

final countries = CountryCoder.instance;
countries.load(); // initialize the instance, does nothing the second time

// Find a country's 2-letter ISO code by longitude and latitude
final String? code = countries.iso1A2Code(lon: -4.5, lat: 54.2);

// Get a full info on a country
final gb = countries.region(query: 'UK');
assert(gb == countries.region(query: '.uk'));
assert(gb == countries.region(lon: -4.5, lat: 54.2));

// Specify level if you need a sub-territory
final im = countries.region(lon: -4.0, lat: 54.2, level: RegionLevel.territory);
assert(im.name == 'Isle of Man');

// Useful convenience methods!
assert(!countries.isInEuropeanUnion(query: 'GB'));

// Which is equivalent to
assert(countries.isIn(query: 'DE', outer: 'EU'));

// And some country info
assert(countries.drivingSide(query: 'UK') != countries.drivingSide(query: 'CH'));

Location Matcher

When you have objects associated with groups of countries, you define these via a LocationSet. Usually you don't instantiate it, but read from a GeoJSON property. For a description of the locationSet structure, see the location-conflation library documentation. All the features are supported, but this class does not produce any geometries.

Use it like this:

// You can pass additional GeoJSON features, with ids ending in ".geojson"
final matcher = LocationMatcher(features);

final locationSet = LocationSet.fromJson({
  'includes': ['uk'],
  'excludes': ['im', [0.3, 51.5, 60]]
});

bool inLondon = matcher(-0.11, 51.51, locationSet); // false
bool inSheffield = matcher(-1.46, 53.28, locationSet); // true

Point-in-Polygon Index

This library also includes a fast lookup engine for polygons containing a point or intersecting a bounding box. Its data structures are loosely based on GeoJSON geometries. In fact, passing a features list from a GeoJSON's FeatureCollection is the primary mode of its operation:

final features = [
  {
    'geometry': {'type': 'Polygon', 'coordinates': [[[...]]]},
    'properties': {'id': 1, 'name': 'Something'}
  },
  {
    'geometry': {'type': 'MultiPolygon', 'coordinates': [[[...]]]},
    'properties': {'id': 2, 'name': 'Another one'}
  },
];

final query = WhichPolygon(features);

// Query the smallest polygon at a (longitude, latitude) location
final name = query(-30, 41)?['name'];

// Query all polygons at a location
final names = query.all(-30, 41).map((p) => p['name']).toList();

// Query polygons in a bounding box
final inBBox = query.bbox(-30, 41, -28, 51).length;

Upstream

This library is a straight-up port of several JavaScript libraries:

Libraries

country_coder
which_polygon