Google Maps Polyline encoder / decoder.

Location.cs

using System;

public partial struct Location
{
    public static readonly Location Empty;

    static Location()
    {
        Empty = new Location { Latitude = 0, Longitude = 0 };
    }

    public double Latitude { get; set; }
    public double Longitude { get; set; }

    public static bool operator ==(Location l1, Location l2)
    {
        return l1.Latitude == l2.Latitude && l1.Longitude == l2.Longitude;
    }

    public static bool operator !=(Location l1, Location l2)
    {
        return l1.Latitude != l2.Latitude || l1.Longitude != l2.Longitude;
    }

    public override bool Equals(object obj)
    {
        return obj is Location && this == (Location)obj;
    }
}

Polyline.cs

// https://developers.google.com/maps/documentation/utilities/polylinealgorithm

using System;
using System.Collections.Generic;
using System.Text;

public static class Polyline
{
    public static string Encode(IEnumerable<Location> points)
    {
        var sb = new StringBuilder();
        var prev = Location.Empty;
        foreach (var pt in points)
        {
            sb.Append(Encode(pt.Latitude - prev.Latitude));
            sb.Append(Encode(pt.Longitude - prev.Longitude));
            prev = pt;
        }
        return sb.ToString();
    }

    public static string Encode(double value)
    {
        if (value < -180 || value > 180) throw new ArgumentOutOfRangeException();
        var val = (int)Math.Round(value * 1e5);
        val = val >= 0 ? val * 2 : (-val) * 2 - 1;
        byte[] buf = new byte[5];
        for (var i = 0; i < 5; i++)
            buf[i] = (byte)((val >> (i * 5)) & 0x1f);
        for (byte i = 5, j = 0; i-- > 0;)
            if ((buf[i] |= j) != 0) j = 0x20;
        var sb = new StringBuilder(5);
        for (var i = 0; i < 5 && buf[i] != 0; i++)
            sb.Append((char)(buf[i] + 63));
        return sb.ToString();
    }

    public static IEnumerable<Location> Decode(string value)
    {
        var loc = Location.Empty;
        var latFlag = true;
        foreach (var t in DecodeInternal(value))
        {
            if (latFlag)
                loc.Latitude += t;
            else
            {
                loc.Longitude += t;
                yield return loc;
            }
            latFlag = !latFlag;
        }

        if (!latFlag)
            throw new ArgumentException("Unexpected end of data.");
    }

    static IEnumerable<double> DecodeInternal(string value)
    {
        int i = 0, j = 0;
        foreach (var t in value)
        {
            var c = (byte)(t - 63);
            j |= (c & 0x1F) << (5 * i++);
            if ((c & 0x20) == 0)
            {
                var n = (j & 1) == 1;
                j >>= 1;
                if (n) j = -(j + 1);
                yield return j / 1e5d;
                i = j = 0;
            }
        }
    }
}