Screen Shot 2013-07-02 at 8.59.53 AMIn a nutshell: an encoded polyline is a set of coordinate pairs (of a line or shape) which have been converted to an ASCII string to significantly reduce the overall size of the data. Now that we have a gist of what we’re talking about, let’s go into some detail.

Encoded polylines are used to store large sets of coordinate data to project a line or shape on a map, typically a Google Map. The encoded polylines are created from sets of coordinate pairs and are fed through an algorithm. Google has a very technical explanation of how the algorithm works, but most of it is gibberish to me. If you do read through it, you can skip the section on levels, as they were deprecated in Google Maps API v3.

Boiled down, what the algorithm does, is take the difference between two coordinate pairs, does some black magic with binary values, and converts that binary value to ASCII characters. Each ASCII character holds eight bits of data, so the savings adds up.

Let’s try a practical example. Continue reading