rgeo

Rgeo is a fast, simple solution for local reverse geocoding, Rather than relying on external software or online APIs, rgeo packages all of the data it needs in your binary. This means it will only ever work down to the level of cities , but if that's all you need then this is the library for you.

Rgeo uses data from naturalearthdata.com, if your coordinates are going to be near specific borders I would advise checking the data beforehand (links to which are in the files). If you want to use your own dataset, check out datagen.

Key Features

• Fast - So I haven't actually benchmarked other reverse geocoding tools but on my laptop rgeo can run at under 800ns/op.
• Local - Rgeo doesn't require pinging some API, most of which either cost money to use or have severe rate limits.
• Lightweight - The rgeo repo is 32MB, which is large for a Go package but compared to the 800GB needed for a full planet install of Nominatim it's miniscule.

Installation

Download with

go get github.com/sams96/rgeo

and add

import "github.com/sams96/rgeo"

to the top of your Go file to include it in your project.

Usage

r, err := New(Provinces10, Cities10)
if err != nil {
	// Handle error
}

loc, err := r.ReverseGeocode([]float64{141.35, 43.07})
if err != nil {
	// Handle error
}

fmt.Println(loc)
// Output: <Location> Sapporo, Hokkaidō, Japan (JPN), Asia

First initialise rgeo using rgeo.New,

func New(datasets ...func() []byte) (*Rgeo, error)

which takes any non-zero number of datasets as arguments. The included datasets are:

• Countries110 - Just country information, smallest and lowest detail of the included datasets.
• Countries10 - The same as above but with more detail.
• Provinces10 - Includes province information as well as country, so can still be used alone.
• Cities10 - Just city information, if you want provinces and/or countries as well use one of the above datasets with it. Once initialised you can use ReverseGeocode on the value returned by New, with your coordinates to get the location information. See the Go Docs for more information on usage.

Then use ReverseGeocode to get the location information of the given coordinate.

func (r *Rgeo) ReverseGeocode(loc geom.Coord) (Location, error)

The input is a geom.Coord, which is just a []float64 with the longitude in the zeroth position and the latitude in the first position (i.e. []float64{lon, lat}). ReverseGeocode returns a Location, which looks like this:

type Location struct {
	// Commonly used country name
	Country string `json:"country,omitempty"`

	// Formal name of country
	CountryLong string `json:"country_long,omitempty"`

	// ISO 3166-1 alpha-1 and alpha-2 codes
	CountryCode2 string `json:"country_code_2,omitempty"`
	CountryCode3 string `json:"country_code_3,omitempty"`

	Continent string `json:"continent,omitempty"`
	Region    string `json:"region,omitempty"`
	SubRegion string `json:"subregion,omitempty"`

	Province string `json:"province,omitempty"`

	// ISO 3166-2 code
	ProvinceCode string `json:"province_code,omitempty"`

	City string `json:"city,omitempty"`
}

So, to put it all together:

r, err := rgeo.New(Countries110)
if err != nil {
	// Handle error
}

loc, err := r.ReverseGeocode([]float64{0, 52})
if err != nil {
	// Handle error
}

fmt.Printf("%s\n", loc.Country)
fmt.Printf("%s\n", loc.CountryLong)
fmt.Printf("%s\n", loc.CountryCode2)
fmt.Printf("%s\n", loc.CountryCode3)
fmt.Printf("%s\n", loc.Continent)
fmt.Printf("%s\n", loc.Region)
fmt.Printf("%s\n", loc.SubRegion)

// Output: United Kingdom
// United Kingdom of Great Britain and Northern Ireland
// GB
// GBR
// Europe
// Europe
// Northern Europe

Data inaccuracy

If you have troubles resolving the location of the coordinates due to GPS and/or data inaccuracy (e.g. at the coast, GPS might give you coordinates of a location several meters out in the water) you can use ReverseGeocodeSnapping instead of ReverseGeocode.

func (r *Rgeo) ReverseGeocodeSnapping(loc geom.Coord) (Location, error)

It first tries to find the location using ReverseGeocode and only if that fails, it will look up the closest location in a default radius of 5km. This radius can be set via the SetSnappingDistanceEarth and SetSnappingDistanceCustom functions.

func (r *Rgeo) SetSnappingDistanceEarth(d float64)
func (r *Rgeo) SetSnappingDistanceCustom(d float64, radius float64)

SetSnappingDistanceEarth takes the radius float64 in km, which is the search radius of the alternative location. If the dataset contains geo-data of a sphere that has different dimensions than earth, use SetSnappingDistanceCustom with the distance d float64 in the same units used for the radius of the sphere.

Contributing

Contributions are welcome, I haven't got any guidelines or anything so maybe just make an issue first.

Projects using rgeo

• rgeoSrv - rgeo as a microservice