A hazard map depicts where a natural hazard — flooding, landslides, ground shaking, volcanic activity, coastal inundation — is likely to occur, and often with what intensity or frequency. It describes the physical phenomenon itself, not the consequences to people or assets.
What it shows
Hazard maps typically combine probability and magnitude. A flood hazard map may show inundation extents for given return periods (e.g., the 1-in-100-year flood); a seismic hazard map shows expected peak ground acceleration with a probability of exceedance; a landslide susceptibility map ranks terrain by its propensity to fail based on slope, geology, and hydrology. Outputs are usually classed or continuous raster surfaces over the area of interest.
Why it matters
Hazard maps are the physical-science foundation for planning, insurance, and engineering decisions. In GIS they are built by combining conditioning factors — slope and aspect from a DEM, lithology from geological maps, rainfall, distance to faults — through weighting, statistical, or physically based models. They feed directly into siting, route screening, and environmental studies.
Hazard map vs risk map
This is the key distinction. A hazard map describes the threat's likelihood and intensity alone. A risk map combines hazard with exposure (people, buildings, infrastructure in harm's way) and vulnerability (how badly they would be affected). Two locations can share identical landslide hazard yet have very different risk if one is uninhabited. Conflating the two overstates or understates the actual stakes.
Concrete example
A landslide susceptibility layer might reclassify slope (from a DEM via gdaldem slope), lithology, and distance-to-stream into ranked classes, then sum weighted rasters into a 1–5 susceptibility index. Crucially, label the output as hazard or susceptibility, not risk, unless exposure has been folded in.