President Hughes bought about 70 GPS (global positioning system) units to use in the mission so that the missionaries could get a reading on every household in their areas.These GPS coordinates can also be used on the ward maps on lds.org.  These are the same units used by hikers so they can find their way in the mountains.  Metro Manila isn't in the mountains but a GPS can help find a member's home when there are few street names or house numbers.