Google Planimeter really needs a better name. Had no idea what a planimeter was until I looked it up. Anyways, obscure name aside, the Google Planimeter lets you guesstimate the size of a lot, block, or other bounded area of land. Using the Google Maps API, Google Planimeter lets you mark some coordinates on a map with the familiar Google Maps interface. So, you can alternate between map, satellite and hybrid view, just like on the Google website itself.
When you click on the map, the Google Planimeter display a flag. Set three flags, and the Google Planimeter calculates the area between the three coordinates. As you set additional flags, the Google Planimeter recalculates the area each time.
Of course, you’re not going to get the same degree of accuracy as when you hire a surveyor. But, for a quick and dirty estimate, this is the place to go. The real fun begins when in satellite or hybrid view. You can guesstimate the square footage of people’s houses, pools, basketball courts with this tool. Works better where Google has provided high magnification maps.