Find the correct US perimeter product
The National Interagency Fire Center map directory separates current-fire tools from historical maps and downloadable data. That distinction matters when a search result takes you to a past season. Read the dataset title and year before searching for an incident. A familiar fire name on an old map does not establish that the same fire is currently active.
NIFC's Wildland Fire Open Data overview explains the public perimeter service and its role alongside other incident information. A perimeter is a mapped boundary belonging to a particular observation or mapping time. An incident point locates a record; a satellite hotspot locates a thermal detection. Three different shapes can refer to the same incident without covering the same area or being updated together.
Why two outlines can look different
Before interpreting a larger outline as new growth, compare the incident identifier, perimeter timestamp and dataset. One image may show a different mapping update or an archived boundary. If the viewer provides several perimeters, retain the dates rather than flattening them into one unexplained polygon. A web page refreshed this morning can still contain a boundary mapped earlier.
For incident descriptions, the Forest Service's InciWeb overview points readers to official incident information. Read the incident's own update and map documents alongside the perimeter dataset. If the public incident site is temporarily unavailable, say that the update could not be checked; do not treat a retained outline as confirmation of today's conditions. Text updates and map files may have different publication times.
Keep evacuation information separate
A fire perimeter and an evacuation zone have different purposes. Never relabel a fire polygon as the area where people have been told to leave. Use the responsible local emergency authority for evacuation alerts, orders and road restrictions. Likewise, a location outside a perimeter is not certified safe by that geometry. This article is a guide to reading sources, not a route planner or emergency assessment.
The PocketWorld wildfire explorer shows available satellite thermal detections, not the complete NIFC perimeter inventory. To compare the two, identify the fire and then preserve both sources' times and legends. Hotspots near an outline are not a substitute for its surveyed or mapped boundary. For a shareable comparison, include the incident identifier, perimeter date, dataset year and link to the official incident update. This makes the evidence reproducible and avoids suggesting that every visible dot is a newly expanding section of the same fire.
Data sources
References are linked beside the explanations above. This evergreen guide does not report current incidents.