This layer contains fire perimeters that are submitted to GeoMAC by field offices. The fire perimeters are updated every one or two days, as the data is made available. If we have received no new data, the "expired" layer is not replaced. The layer is replaced as soon as we receive an updated file. Perimeters are usually collected on a daily basis for large fires that are growing. However, there may be gaps in daily coverage.
Perimeters are collected in the field by a variety of means, including infrared flights, and by using a GPS unit to map the perimeter. Please NOTE: GeoMAC only displays perimeter data as they are submitted by field offices. Since data are not received for all fires, you may not be able to view perimeters for every fire.
A perimeter is displayed in one of two ways depending upon how old it is. Once a perimeter is more than two days old, or is replaced by a more current perimeter, it is displayed in blue-gray in the Previous Perimeters layer. Also, perimeters are usually no longer collected in the field once a fire is no longer growing in size and is mostly contained.