NASA FIRMS Wildfire Map Explained: Hotspots and FRP

NASA FIRMS (Fire Information for Resource Management System) is NASA's service for distributing satellite detections of active fires and thermal anomalies. Each dot on a FIRMS-based wildfire map is a hotspot: a satellite pixel where an infrared sensor measured heat consistent with fire. It tells you that something was hot in that pixel when the satellite passed over, not exactly where the fire edge is.

That distinction explains almost every question people have about fire maps. Why does a fire look bigger on the map than in photos? Why does a factory show up as a fire every night? Why did a fire not appear until hours later? The answers come from pixel size, satellite timing and how the detection algorithm works.

This guide explains which satellites feed FIRMS, what a hotspot represents, how fresh the data is, what fire radiative power and confidence mean, where false positives come from, how hotspots differ from fire perimeters, and how to read the fire layer on GodsView AI.

Open the live wildfire map

What is NASA FIRMS?

FIRMS is part of NASA's LANCE (Land, Atmosphere Near real-time Capability for EO) system. The FIRMS site says it was originally developed by the University of Maryland with funding from NASA's Applied Sciences Program and moved to LANCE in 2012. It offers a global Fire Map, a US/Canada Fire Map, downloads in formats such as shapefile, KML and text, email alerts, web services and archived data.

Many third-party maps, including GodsView, show FIRMS detections. GodsView loads NASA FIRMS active fires about every 10 minutes, and the layer is free to view. The full source list is on the methodology page.

Which satellites detect fires for FIRMS?

FIRMS combines data from several instruments on polar-orbiting satellites. The FIRMS FAQ lists MODIS on Terra and Aqua, VIIRS on Suomi NPP, NOAA-20 and NOAA-21, and Landsat.

Polar-orbiting instruments typically give two overpasses a day at a given location, with more frequent coverage toward the poles. With several satellites in service, most places are observed a few times a day, but there are still gaps of several hours between looks.

MODIS vs VIIRS: which should you trust?

Neither is "right"; they are different measurements. VIIRS has smaller pixels and, per the FIRMS FAQ, a greater response over small fires. MODIS has a longer record, which matters when you compare this season with past years. If both show detections in the same place, that is stronger evidence than either alone.

What does a hotspot dot actually represent?

This is the most important concept on any fire map. According to the FIRMS FAQ, each hotspot or active fire detection represents the center of a pixel flagged as containing one or more fires. The fire itself is often much smaller than the pixel.

In practice, that means:

• A single VIIRS dot stands for a ground area of roughly 375 by 375 meters, and the fire inside it could be a fraction of that.
• A MODIS dot stands for roughly a square kilometer.
• Pixel size is not identical for every detection. The FIRMS data includes scan and track values that give the actual pixel dimensions for each one.
• Clusters of dots show where heat was detected, but the gaps between them are not proof of unburned ground.

FIRMS states that MODIS can routinely detect both flaming and smoldering fires of about 1,000 square meters, and under very good conditions fires as small as 50 square meters. So small fires can show up, but the dot will always be larger than the flames.

How fresh is FIRMS fire data?

FIRMS publishes several latency tiers. The FIRMS FAQ describes them as:

Two delays add up on any map. First, the satellite has to pass over the fire, which may be hours after it started. Second, the detection has to be processed and published. Then the map you are using refreshes on its own cycle; GodsView checks FIRMS about every 10 minutes.

The acquisition date and time of each detection is recorded in UTC. When a fire is moving fast, look at that timestamp rather than assuming the dot is current.

What does FRP (fire radiative power) mean?

Fire radiative power is the rate of radiant heat energy coming from the fire or fires in a pixel, measured in megawatts (MW). The FIRMS attribute reference describes it as pixel-integrated FRP.

FRP is widely used as a proxy for fire intensity and is related to how fast vegetation is burning and how much smoke is being produced. On a map, higher FRP values usually mean a more intense fire in that pixel. One caution applies: FRP describes heat output at the moment of the satellite pass, not the total area burned or how long the fire has been going.

What do FIRMS confidence levels mean?

Confidence is the detection algorithm's estimate of how likely a detection is to be a real fire. The two main instruments report it differently:

• VIIRS uses three classes: low, nominal and high. FIRMS notes that low-confidence daytime VIIRS pixels are typically associated with sun glint and a weaker temperature anomaly.
• MODIS reports a value from 0 to 100 percent, which can be grouped into low, nominal and high classes.

The FIRMS FAQ says confidence should be used with caution. A sensible approach is to treat high and nominal detections as likely fires and to look for corroboration, such as repeat detections on later passes, before relying on low-confidence ones.

Day or night detection

Each detection also carries a daynight flag, D for a daytime detection and N for a nighttime one. Because low-confidence VIIRS detections are linked to daytime sun glint, it is worth checking this flag when a lone low-confidence dot appears in the afternoon.

Why do some hotspots appear where there is no wildfire?

Not every hotspot is a wildfire. FIRMS documents several sources of false or non-wildfire detections:

• Static heat sources. Petrochemical plants, cement plants and gas flares are persistently hot and appear night after night.
• Volcanoes. Active lava and vents register as thermal anomalies.
• Sun glint. Reflected sunlight can trigger low-confidence daytime detections.
• Other effects. The FAQ also mentions superheated smoke plumes and satellite calibration maneuvers.

For MODIS standard data, the type attribute helps sort these out: 0 is a presumed vegetation fire, 1 an active volcano, 2 another static land source and 3 an offshore detection. That attribute is not available for VIIRS.

Why fires can be missed

Optical sensors cannot see through clouds, so a fire under thick cloud may not be detected at all. Fires that start and burn out between satellite passes, and fires too small to register in a pixel, can also go unrecorded. The absence of a dot is never proof that there is no fire.

See fires on the 3D globe

Hotspots vs fire perimeters: what is the difference?

A hotspot is an automated satellite detection of heat. A fire perimeter is a mapped boundary of an incident, drawn and reported through interagency fire-management systems. In the United States, current perimeters are published by the National Interagency Fire Center's WFIGS group through the NIFC Open Data site.

The two work best together. Hotspots outside an older perimeter can indicate new growth since the perimeter was last mapped. On GodsView, FIRMS hotspots are free, and NIFC fire perimeters are part of GodsView Pro.

How to read the wildfire layer on GodsView

1. Open the live wildfire map, or turn on the fires layer from the main map.
2. Zoom to a region of interest; regional pages such as California wildfires, Canada wildfires and Australia wildfires are a quick start.
3. Look at how detections cluster, and remember that each dot is a pixel center, not a flame front.
4. Add the free wind overlay to see which way smoke is likely to drift; weather radar for rain over the area is a Pro layer.
5. With GodsView Pro, add NIFC perimeters, air quality (CAMS and sensor.community) and alerts for fires, delivered in-app, by browser push or email.

Four checks before you share a fire detection

Fire dots spread quickly on social media, often without context. Before you repost one or cite it in a report, run through four quick checks:

1. Time. Read the acquisition time in UTC and convert it. A detection from the previous night is not a current fire front.
2. Location type. Switch to the satellite basemap and look at what is under the dot. A refinery, a flare stack or a volcano is a known heat source.
3. Repetition. Look for detections from more than one pass or more than one instrument. A single low-confidence pixel is weak evidence.
4. Official confirmation. Check whether a fire agency or local authority has reported an incident in that area.

Teams that use fire data for exposure monitoring can read more on the insurance and risk page. Fire detections also flow into the Ops Center alongside other hazards.

What a satellite fire map cannot tell you

FIRMS is a valuable global dataset, and its limits are well documented by NASA:

• It does not show the fire edge. Dots are pixel centers, and the real fire is usually smaller than the pixel.
• It is not live video. Detections depend on satellite passes and processing time.
• It misses some fires. Clouds, canopy and timing gaps all hide fires.
• It includes some non-fires. Industrial sites, flares and volcanoes appear as hotspots.
• It does not tell you what is safe. A map cannot tell you whether a road is open or whether to leave.

For safety decisions, follow your local fire service, emergency management agency and official evacuation orders. Do not use any satellite fire map, including this one, to decide when or where to evacuate.

If you work with public data more broadly, our guides to what OSINT is and using live maps as a journalist cover verification habits. For how other Earth data is presented, see how to read an earthquake map, and for how the satellites behind FIRMS are tracked, see how satellite tracking works.

The short version

A FIRMS hotspot is a pixel where a satellite measured fire-like heat. VIIRS gives 375-meter detail, MODIS about one kilometer and Landsat 30 meters over North America. Global data typically arrives within about three hours of a pass. Use FRP for relative intensity, confidence to filter doubtful detections, and the acquisition time to judge freshness. Compare hotspots with official perimeters, and leave safety decisions to the agencies responsible for them.

Open the live wildfire map