A port of this PHP code: http://stackoverflow.com/questions/1763917/google-static-maps-move-maps-with-a-finger To C# in Unity3D to convert google maps lat/lng to pixel coordinates and vice versa.

MapUtils.cs

using UnityEngine;
using System.Collections;

public class MapUtils {
  
	static float GOOGLEOFFSET = 268435456f;
   	static float GOOGLEOFFSET_RADIUS = 85445659.44705395f;//GOOGLEOFFSET / Mathf.PI;
   	static float MATHPI_180 = Mathf.PI/180f;

   static private float preLonToX1 = GOOGLEOFFSET_RADIUS * (Mathf.PI/180f);

   public static int LonToX( float lon ) {
     return ((int)Mathf.Round(GOOGLEOFFSET + preLonToX1 * lon));
   }

   public static int LatToY( float lat ) {
     return (int)Mathf.Round( GOOGLEOFFSET - GOOGLEOFFSET_RADIUS * Mathf.Log((1f + Mathf.Sin(lat * MATHPI_180)) / (1f - Mathf.Sin(lat * MATHPI_180))) / 2f);
   }

   public static float XToLon( float x) {
     return ((Mathf.Round(x) - GOOGLEOFFSET) / GOOGLEOFFSET_RADIUS) * 180f/ Mathf.PI;
   }

   public static float YToLat( float y) {
     return (Mathf.PI / 2f - 2f * Mathf.Atan(Mathf.Exp((Mathf.Round(y) - GOOGLEOFFSET) / GOOGLEOFFSET_RADIUS))) * 180f / Mathf.PI;
   }

   public static float adjustLonByPixels( float lon, int delta, int zoom) {
     return XToLon(LonToX(lon) + (delta << (21 - zoom)));
   }

   public static float adjustLatByPixels( float lat,  int delta, int zoom) {
     return YToLat(LatToY(lat) + (delta << (21 - zoom)));
    }
}