The white pins mark fields I know the geese have consumed in whole or in part. There are probably others I haven't heard about, because the very persistence of the geese has rendered them no longer newsworthy --except to you, personally, when they start eating your particular school yard. And they are getting close! I noticed today that they have progressed to the school marked by the pink pin. Only another half-mile or so and they will have feasted throughout the entire suburban area.
Suburbanites are renowned for their love of great expanses of Kentucky bluegrass, and are equipped to deal with dandelions, crab grass, even moles. This winged white plague from the sky --we never saw it coming.
See here for snow geese 2008-09.