Encoding polylines for Google Maps

If you want to display complicated path data on a Google Map, the most efficient way to do so is with an encoded polyline or polygon. The primary purpose of this page is to explain this encoding process. Most people interested in this discussion will be mathematically literate javascript programmers with a specific interest in the Google Maps API. A secondary purpose of this page is to provide some basic utilities to perform the encoding and only a passing familiarity with the Google Maps API is needed to use the code produced here.

Encoding utilities

• Encoding form: Convert path data to the encoded format. Can generate code or a map.
• Point and click: A Google Map containing a point and click interface to the encoding algorithm.
• Decoder: Decode an encoded point string to obtain a sequence of lat/lng values.
• The PolylineEncoder class: Dynamically encode polylines on the fly.

Discussion

• A description of encoded polylines
• Example encoded polylines
• Example encoded polygons
• An explanation of the algorithm
• Potential pitfalls

Ports

The polyline encoder has been implemented in several other programming languages. I have only used the Mathematica code, but the other programs appear to be direct ports of the code written here.

• Perl by Marcelo Montagna and John Coryat
• Ruby by Joel Rosenberg
• PHP by Jim Hribar
• Java by Mark Rambow
• Mathematica by me