The page remembers your most recent position/zoom/map-type for the
next time you visit.
If you haven't visited before, it tries to figure out your location
based on your internet address.
The area computation is done using spherical geometry, so it's
correct for large regions.
The lines between points are drawn as great circles, to go along
with the spherical area math.
Lines that cross the International Dateline do work, with
a small gap in the line.
(Google Maps applications tend to have problems with the Dateline.)
Areas that span more than half the globe may display strangely.
This used to be called the Google Areometer, because I couldn't
remember the name of the doohickey used to measure areas on a map.
But the Lazyweb reminded me, so I changed it.
Links using the old name will continue to work.