What is an encoded polyline?

An encoded polyline is a compact string that stores a series of coordinates, used by Google Maps and many routing APIs to transmit a path efficiently instead of a long array of numbers.

Why are deltas encoded instead of absolute values?

The algorithm stores the difference between each point and the previous one. Because consecutive points are close, the deltas are small and compress to fewer characters than full coordinates.

What does precision 5 versus 6 mean?

Precision 5 multiplies coordinates by 100000, the Google default, giving about a metre of resolution. Precision 6 multiplies by 1000000 for finer detail and is common in OSRM output. The decoder must use the same precision.

How are negative coordinates handled?

Each delta is shifted left by one bit, and negative values are bitwise inverted. This signed encoding lets the rest of the algorithm treat every value as a chunked base-64 number.

Can I round-trip the result?

Yes. Feed the output into the Google Polyline Decoder at the same precision and you recover the original points, subject only to the rounding implied by the chosen precision.

What is the Google Polyline Encoder?

Encode a list of latitude and longitude points into a Google Maps encoded polyline string. Implements the official signed-value, base-64, delta-encoded algorithm at precision 5 or 6. It runs free in your browser on Gera Tools, with nothing uploaded.

Google Polyline Encoder

Name: Google Polyline Encoder
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

Encoded polylines

A route or shape is naturally a list of coordinates, but sending hundreds of floating-point numbers is wasteful. The Google encoded polyline format squeezes that path into a single short string that map and routing APIs understand directly. A three-point path that would otherwise consume over 50 characters of JSON can compress to as few as 20 ASCII characters.

How the algorithm works, step by step

Scale and round: Multiply each latitude and longitude by 10^precision (100,000 for precision 5, 1,000,000 for precision 6) and round to an integer.
Take deltas: Store the difference from the previous point. The first point uses zero as the previous value, so the string is self-contained.
Sign-encode: Left-shift each delta by one bit. If the value is negative, invert all bits. This packs the sign into the lowest bit.
Chunk and emit: Split the result into 5-bit groups, OR each chunk with 0x20 if more chunks follow, then add 63 to land in printable ASCII.

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

The first point is encoded as a delta from zero, so the string is fully self-contained. Each subsequent point only records how far it moved from the last one, which is why consecutive GPS points — rarely more than a few hundred metres apart — compress so effectively.

Choosing between precision 5 and precision 6

Setting	Multiplier	Resolution	Use when
Precision 5	100,000	~1 metre	Google Maps, Google Directions API, most web maps
Precision 6	1,000,000	~0.1 metre	OSRM, Valhalla, Mapbox Directions, high-accuracy GPS tracks

Mixing precision at encode and decode produces coordinates scaled by 10×, which looks like all points jumping to the wrong location — it is the most common polyline debugging mistake.

Practical tips

Order matters: The encoding is delta-based, so the coordinates must be in path order. Reversing the array produces a valid but backwards route.
Round-tripping: Feed the encoded string into a decoder at the same precision and you recover the original points, subject only to rounding at the chosen precision.
Coordinates per line: This encoder accepts one lat, lng pair per line; commas and spaces between the two numbers are both recognised.
API use: Once encoded, drop the string directly into the polyline parameter of a Google Maps Static API or Directions API call without any additional serialisation.