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Map Comparison Feature 

The map comparison feature lets you visualize the differences between the 2000 and 2007 maps…

Here the Red April 2000 map is overlaid on top of the Yellow June 2007 map. The yellow that is visible shows where the floodplain has become larger.

Likewise when the Yellow panel is displayed on top of the Red you can easily see where the floodplain has been reduced in this example.

Please Note: The streets and other map features may not overlay exactly in some areas. This is due to the fact that FEMA used a different and more accurate base map for the 2007 FIRMs.

If you need assistance in navigating this website and have not viewed the demo video provided please do so by selecting the following link: Demo

Following Information provided by: Harris County Flood Control District, Public Information Fair, November 2004

What are Flood Insurance Rate Maps?

Flood Insurance Rate Maps, also known as FIRMs, are published by the Federal Emergency Management Agency (FEMA) to determine flood insurance requirements (as the name implies) and to assist communities in regulating new development.

Among other things, Flood Insurance Rate Maps show areas that have a 1% chance of flooding and a 0.2% chance of flooding in any given year (also known as the “100-year” and “500-year” floodplains). These areas are determined to be the areas of highest risk when a stream overflows its banks or when coastal waters experience tidal surges from tropical storms or hurricanes.

Not All Flood Risks Are Shown

There are other reasons for flooding that are not shown on Flood Insurance Rate Maps:

•  Actual rainfall amounts may exceed those assumed in the computation of mapped floodplain. In Harris County, the 1% floodplains are based upon a rainfall of about 13 inches in 24 hours.
•  Intense rainfalls can overwhelm local drainage systems - causing water to pond deeply in the streets or flow overland to the nearest stream, flooding homes along the way.
•  Smaller channels may not have been studied. The stream near your home may have a floodplain that is not shown on the Flood Insurance Rate Maps.
•  The Flood Insurance Rate Maps are estimates using the best technology and engineering tools, but nature can be unpredictable.

Remember, 65% of the area that flooded during Tropical Storm Allison was outside of the mapped regulatory floodplain. Nationwide, one-third of the flood loss claims are from property located outside of the mapped 1% (100-year) floodplain.

What’s On a Flood Insurance Rate Map?

A Flood Insurance Rate Map will show several things, but most importantly it shows the areas of the highest risk of flooding caused by streams and tidal surge. Some of the information includes:

•  1% Floodplain (Zones AE, A, AO, and V)
•  Base Flood Elevations (elevation above mean sea level that the 1% flood reaches)
•  0.2% Floodplain (Zone X Shaded)
•  Floodway
•  Corporate Limits
•  Streets and Highways
•  Engineering information such as survey benchmarks and the location of cross sections used in computer simulations.

What do the Zones Mean?

The following table shows the different zones on the Flood Insurance Rate Maps and what they mean.

The legend on the Flood Insurance Rate Map has a more detailed description of the zones.


Common Name


Level of Risk

Insurance Required*

Zone AE

1% (100-year) Floodplain

Dark Gray

1% Chance or Greater



1% (100-year) Floodplain

Hatched Dark Gray

1% Chance or Greater


Zone VE

1% (100-year) Coastal Floodplain

Dark Gray

1% Chance or Greater


Zone X Shaded

0.2% (500-year) Floodplain

Light Gray

Between a 0.2% and a 1% chance


Zone X

Areas Outside the Floodplain

White (no color)

Less than a 0.2% chance


*Insurance may be required by your lender if you have a federally-backed mortgage.

Note: Zones A and AO are also 1% (100-year) floodplains, but they do not have detailed base flood elevations like Zone AE. There are other zones on the Flood Insurance Rate Maps that are explained in the legend.


  © 2012 - Walter P. Moore & Associates, Inc. - Houston, TX, USA