What does the decoder produce?

It produces the ordered list of latitude and longitude points that were encoded, one per line. Each line is a single coordinate of the original path.

Why must I choose the right precision?

The encoder scaled each coordinate by ten to the precision. Decoding with the wrong precision multiplies or divides every value by a power of ten, putting the points in the wrong place. Match the source exactly.

What precision do common APIs use?

The Google Directions and Maps APIs use precision 5. OSRM version 5 and several other routing engines use precision 6. If unsure, try 5 first and check that the coordinates look plausible.

What happens with an invalid string?

Each character must fall in the base-64 range used by the format. If the string ends mid-value or contains a character outside that range, the tool reports the error instead of producing garbage points.

Can I re-encode the points?

Yes. Paste the decoded points into the Google Polyline Encoder at the same precision to reproduce the original string, allowing for the rounding inherent in the format.

Google Polyline Decoder

Decoding a polyline

Routing and mapping APIs return paths as a single encoded polyline string to save bandwidth. This tool turns that string back into the list of coordinates so you can plot, inspect or process the route yourself.

How it works

The decoder walks the string character by character. It subtracts 63 from each character, strips the continuation bit (0x20), and accumulates 5 bit chunks until a chunk without the continuation bit ends the value. That signed integer is the delta from the previous coordinate; it is un-shifted and inverted if odd to recover the sign.

_p~iF~ps|U_ulLnnqC_mqNvxq`@
  ->  38.5, -120.2 / 40.7, -120.95 / 43.252, -126.453

Latitude and longitude alternate, and each running total is divided by ten to the precision to produce the final coordinate.

Example and tips

If the decoded points land in the ocean or far from where you expect, the precision is almost certainly wrong, so toggle between 5 and 6. The values are returned in path order, exactly as encoded. Because the format is lossy at the chosen precision, decoding then re-encoding may differ by a unit in the last decimal place, which is normal.