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Featured Item: National Flood Hazard Layer: Iowa

 By Jay Bowen

Featured Item: National Flood Hazard Layer: Iowa

With flooding a perennial problem in the low-lying riverine areas of Iowa, the National Flood Hazard Layer: Iowa is a particularly useful resource for Iowans. This dataset is managed by the Iowa Department of Natural Resources on the Iowa Geodata website. From this dataset, you can download the National Flood Hazard Layer, which includes the Iowa portion of the regulatory dataset produced by FEMA for their Flood Insurance Rate Map (FIRM). It is particularly useful to community officials and members of the public who wish to know which parts of their communities are within areas FEMA defines as having a 1-percent-annual-chance for a flood event, a 0.2-percent-annual-chance flood event, or minimal flood risk. In this post, I will take a look at one presentation of the data in an interactive online map.

I live in Iowa City, in Johnson County. By downloading the data as a geodatabase, I can open it in QGIS, extract the features within Johnson County, and export a GeoJSON file for use in an online map. The resulting file is quite large, so potential users may wish to look into a few ways to handle large file sizes by using different data formats or employ preferred methods of reducing the size of the exported GeoJSON file.

Incorporating, styling, and formatting the data for online use with JavaScript, CSS, and HTML, we can see how this data can be presented in a more user-friendly format. This can then be shared with any number of stakeholders in flood-related planning or mitigation efforts. Here, the map has been furnished with a legend describing the relevant flood risk classes in Johnson County, popup content further clarifying these classes when the user clicks on a flood zone, and an information button in the top-right corner explaining the map and data sources. Users can zoom out to see Johnson County in its entirety or zoom in for a closer look at their neighborhood or property. To see the data and code behind this map, you can take a look at the GitHub repository here.

Flood zone in Iowa

Iowa's flood hazard layer

What BTAA Library submitted the item?

University of Iowa

Interesting tidbits:

  • Shows the location of Flood Insurance Rate Map (FIRM) Flood Hazard Boundaries
  • Useful for determining the relative risk of flooding across Iowa

Where can I find out more?

  • University of Iowa Libraries
  • Digital Scholarship & Publishing Studio, University of Iowa
Have questions about this item, the BTAA geoportal, or maps and geospatial data in general? Please don’t hesitate to contact our project team

Jay Bowen is the GIS Specialist at the Digital Scholarship & Publishing Studio, University of Iowa Libraries.