Guide · Elevation
Elevation and contours for a Florida lot, without GIS software
Turn on 5-foot contours over the lot: they come from the state's LiDAR survey and show its high and low ground to within a few feet. Add a shaded relief from USGS's 3D Elevation Program to see ridges, swales and depressions. Then set the ground against the flood map: zone AE gives a base flood elevation to compare with, zone A gives none, and only an elevation certificate measures the building that counts.
Step 1: read the contours across the lot
A contour joins points of equal ground height. The statewide set we use is the Florida Division of Emergency Management's 5-foot contours, drawn from LiDAR, a laser survey flown from aircraft: 732,089 lines across the state. Each is labelled with its height in feet.
- No line crosses the lot. The whole lot sits within one 5-foot band. Common on Florida's flatwoods; it tells you the lot is flat, not how high it is to the inch.
- One or two lines cross it. The lot falls 5 feet or more from one side to the other. Note which side is high: that is where a house pad and a drainfield usually go.
- A closed ring with the ground falling inside. A depression: a pond, a borrow pit, or in the karst counties of the centre and north, possibly a sinkhole. Ask the county what it knows.
Step 2: shade the relief
Contours miss the small shapes. A hillshade, the ground lit from several directions, shows ditches, old dunes, berms and drainage paths a 5-foot interval cannot. The USGS 3D Elevation Program (3DEP) publishes Florida's bare-earth ground model, and USGS draws the hillshade on its own server. An elevation tint does the same job in colour: green near sea level to brown at higher ground.
Step 3: get exact heights when you need them
For a number rather than a picture, the 3D Elevation Program says all its products are free and without use restrictions. On The National Map Downloader, draw a box around the lot and choose a 1-meter DEM or the LiDAR point cloud. Opening those does take GIS software; for a buying decision, the contours and the relief usually say enough.
Step 4: compare the ground with the flood
Elevation and flood zone answer different questions. The ground height is where the land is. The base flood elevation (BFE) is how high FEMA expects water to rise in the 1-percent-annual-chance flood. A lot whose ground sits above the BFE is in a better position than its zone suggests; one below it needs fill or a raised floor to build.
FEMA's glossary says the catch: zone AE provides base flood elevations, while in zone A "no depths or base flood elevations are shown". Inland, zone A is common, and there the contours are the only clue you have before you pay a surveyor.
| County, parcels with a FEMA zone | In the 100-year floodplain | Zone AE (a BFE) | Zone A (no BFE) | In the category 1 surge zone | Category 1 surge, outside the floodplain |
|---|---|---|---|---|---|
| Polk, 414,796 | 48,408 | 12,077 | 36,187 | 0 | 0 |
| Marion, 280,214 | 15,408 | 5,034 | 10,372 | 32 | 4 |
| Levy, 46,930 | 7,416 | 4,081 | 2,461 | 4,170 | 93 |
| Wakulla, 25,689 | 8,379 | 3,999 | 1,661 | 5,765 | 74 |
| Gulf, 18,348 | 9,484 | 6,983 | 1,246 | 4,066 | 48 |
| Pinellas, 326,477 | 82,212 | 77,038 | 3,148 | 78,471 | 6,791 |
| Lee, 463,747 | 142,428 | 133,885 | 2,490 | 141,650 | 34,214 |
| Monroe, 81,468 | 74,842 | 67,801 | 0 | 51,560 | 255 |
In Polk, three of every four floodplain parcels are in zone A, with no BFE on the map; in Marion, two of three. On the coast the gap runs the other way: in Lee, 34,214 parcels are in the category 1 storm surge zone, the first to flood in a hurricane, but outside FEMA's 100-year floodplain. Statewide, 265,221 parcels are in zone A, and 926,906 sit in the category 1 surge zone.
Where the map stops
- The interval. Five feet is a lot of water. Two lots between the same pair of lines can differ by four feet.
- The date. LiDAR records the ground when it was flown. Fill, a new pond or a graded pad since then is not in it.
- No spot height. Our map draws the contours and the relief; it does not read off the height of a clicked point or draw a profile.
- Ground is not the floor. Flood rules and insurance look at the building. A FEMA elevation certificate, completed by a licensed professional, records that.
On Map Views
In the Layers tab, the Elevation folder holds Contours, 5 ft, drawn from zoom 12 and labelled in feet. The Relief folder holds the USGS hillshade, the tinted elevation and NOAA's land and sea floor, each laid see-through over the map, and Map view offers the USGS topo map as a base. Click the map with the flood zones on and the popup lists the zone's fields, including the base flood elevation where FEMA's map gives one. The parcel report adds the flood zone, the storm surge category, the evacuation zone and the wetland share. For what the zones mean, see flood zone AE, X or VE; for the soil under the same ground, the soil map for septic.
Contours and relief are shown as FDEM and USGS published them, and flood zones as FEMA's effective maps give them. An elevation certificate or a survey by a Florida-licensed professional is the authority on a site's height and a building's floor.