Viewing flood zones with ArcGIS Explorer, Part 1
Problem: You need to look at some GIS data without purchasing a GIS software package.
This post is inspired by a reader question. My friend Jeremy asks,
“Is there any easy way to get at GIS data of water tables, flood zones, and stuff like that? Things that people who buy houses really should look into but seldom do.”
I cut my teeth making flood zone maps so I am quite familiar with where this data lives. I revisited the FEMA Map Service Center to give him some specific advice about where to look. My plan was to determine the easiest/fastest path to the information. To my dismay, the website has not changed much since I changed jobs. Meaning, to put it bluntly: there is no easy way.
I assume most visitors to the website would want to be able to type in an address and have that address come up as a dot on a map with the flood zone layer below it. If the dot falls within a flood zone, they’d be able to tell in one glance. Well, you can get pretty close, but you can’t exactly do that. So, instead of talking about the easiest way to get flood zone information, I’ll talk about four different ways.
I attended college at George Mason University so I decided to use the city of Fairfax as my example location. Pretend you are moving there. Because I don’t want to map a private residence, pretend you are moving there because you just got elected mayor. You want to check if your new digs at City Hall are in danger of flooding.
Method 1: FEMA’s Map Viewer
https://hazards.fema.gov/wps/portal/mapviewer
Pros
- This viewer allows you to type in an address and zoom to it.
- The map that comes up shows the flood zones in that area along with a lot of other useful information.
- There’s an identify tool that allows you access even more information about the data layers.
Here’s what I got for City Hall:
Cons
- There’s no “you are here” symbol on the map. If I’m not familiar enough with the area to already know where City Hall is, I still don’t know whether it’s in a flood zone.
- There’s too many layers turned on by default, which clutters the map, making it confusing and hard to interpret at first glance.
- The legend isn’t very helpful. It doesn’t explain what the blue-hatched Zone A is, or what the purple text LOMRs are. I only know that they are Letters of Map Revision because I used to work there.
Method 2: Product Search by Address…
Box on top-left corner of main Map Service Center screen
You can enter an address and select either a Flood Map (visual image) or DFIRM (digital database) product. The Fairfax City data is at the moment only available as a DFIRM, which I will discuss later in method 4. For now, I’ll enter the address of nearby GMU campus to bring up the Flood Map of surrounding Fairfax County.
Pros
- A beautiful looking map (If I don’t say so myself) which is simple and easy to interpret, and also happens to be the authoritative flood zone representation product.
- A good legend which explains in detail what the flood zone designations mean.
Cons
- Obviously no “you are here” symbol on this static map.
- And, it’s even harder to pinpoint an exact location than in the Map Viewer, because these maps only show major roads, and most of the time use route numbers instead of road names.
It isn’t hard to see why people may feel the need to look elsewhere to determine if their prospective property is really in a flood zone. Maybe that’s why a google search for “flood zone data” brings up companies that will research this for you if you pay them. There are, however, other ways, which are free or almost free.
Method 3: FEMA’s Web Map Service (WMS) & ArcGIS Explorer
https://hazards.fema.gov/femaportal/wps/portal/NFHLWMSe
A web map service is a computer program that will query a database and deliver the results back in the form of a dynamically generated map. FEMA makes the National Flood Hazard Layer available for free through a WMS. You need to have GIS software in order to read WMS data. However, if you don’t have access to the ArcGIS Desktop package that I regularly blog about, you aren’t locked out from playing. You just need to grab a copy of ArcGIS Explorer: “GIS for Everyone” at http://www.esri.com/software/arcgis/explorer/index.html
Once you’ve installed and opened the program, press the Add Content icon on the main toolbar. Select GIS Services… and then press New Server Connection. For the server type, chose WMS, and then enter the Server address that FEMA gives on their tool description page:
http://hazards.fema.gov/wmsconnector/wmsconnector/Servlet/NFHL?
You’ll then be given a list of services to choose from. Flood Hazard Zones (General) is the main one. If you pick that, then enter your address in the Find box on the left side of the screen, the globe will whirl around until you see this.
Eureka! Now I know City Hall isn’t in a flood zone!
(I changed the Basemap to Streets)
Stay tuned, in two weeks I will post about Method 4: Using DFIRM Shapefiles. The best is yet to come.
Tags: ArcGIS Explorer, flood zone, Web Map Service
July 8th, 2010 at 1:51 am
Appreciate you sharing, great blog.Thanks Again. Really Cool.