Geo58js

Yet another short-link specification for geo-coordinates.

Sister library of Geo58 (Python).

Key Features

• uses base-58 encoding
• can be as short as 8 characters, mostly 9 characters
• maximum length of 10 characters
• resolves to about 1.1m accuracy
• geocoordinates that are close, look similar
• can include a zoom level of a map (20-5)

Base58 encoding

Base58 encoding uses 58 alphanumerical characters, 49 of the alphabet plus 9 digits. Characters that look similar ('0', 'O', 'I', 'l') are omitted. This allows for manual copying of data with little potential for ambiguity.

8-10 characters short

The encoding is done in the followin schema: [Zoom 4bit][joined [Lat 25bit][Lon 26bit]]

• Zoom: beeing an optional parameter for a possible viewport (see below).
• posLat: is the latitude (mapped from [-90,90] to [0, 180]).
• posLon: is the longitude (mapped from [-180,180] to [0, 360]).

The last 51 bit are 'intervoven' to generate a bit-sequence with least significant bits to the right. This allows the generation of short-strings that are similar to each other if they are close to one another.

Link similarity

The following 3 short-strings, refer to cafes in Heidelberg, which are only ~25m apart:

• NBiwwcnfq -> { zoom: 19, lat: 49.41054, lon: 8.69964 }
• NBiwwcnuw -> { zoom: 19, lat: 49.41047, lon: 8.69984 }
• NBiwwcnZc -> { zoom: 19, lat: 49.41035, lon: 8.69971 }

Zoom level (can be) included

4 bit of the short-string are used to encode the zoom level of a viewport. This can be used to hint at the size of the object that is being referred to. The zoom level is pre-fixed to the bit-sequence. It is also 'inverted' to allow zoom level 20 to be represented as zero and 19 as one. Zoom level 5 would be using 4 bits.

As the zoom level is pre-fixed, zoom level 20 does not 'consume' any bit-bandwidth, resulting in a short-string being as short as possible.