ArcGIS Online

Flooded by Features? Use This Recipe for Building Complex Hosted Feature Services

For a homeowner, learning that you live in a floodplain can be terrifying, especially if there’s a major hurricane heading your way, like we have seen all too often.

flooded house
House flooded by a hurricane. Image courtesy of FEMA.

For a GIS professional, having to develop a hosted feature service with 2.5 million features can be almost as terrifying. But as a part of the Living Atlas team, that is part of what we do every day.

Recently, we updated the USA Flood Hazard service, which is the official FEMA database of flood risk in the United States, to include both an image service and a hosted feature service.

Why both?

The image service provides faster rendering for visualization and basic mapping applications. The hosted feature service provides access to the many attributes associated with any polygon –  in this case, details about flood risk. However, the more complex the features, the slower the web service responds. Fortunately, improvements in the performance of ArcGIS Server can now handle the demands of such a large and complex dataset.

This blog provides our basic workflow for deploying a complex feature service.

flood map of Houston, TX
Flood hazard map of Houston, TX. Houston is not only extremely vulnerable to flooding, but also has very spatially complex flood zones.

Clean up the attribute table to reduce what needs to be served


Publishing the Service

No one can expect a 10 GB service to publish in a few minutes. But sometimes the publishing process seems to drag on indefinitely. Here’s a trick to get everything to load:

ArcGIS Pro menu for importing features into a file geodatabase


Optimize the Settings

Original FEMA data source: 13.5 GB; 2.5 million features

USA Flood Hazards in the Living Atlas: 6.8 GB;  2.1 million features


Configure the Web Map

One trick in getting a performant web map or app is relying on the strengths of both the image service at coarse resolution and the feature service at higher zoom levels. We adjust the Set Visibility Range of both layers in the web map so that they appear/disappear at the optimal scale. Figuring out the zoom level takes a bit of trial and error, but once you figure out the Goldilocks, you’ll have the best of both worlds.

Check out the USA Flood Hazards web map that combines both the image service and hosted feature service. Please take note that while FEMA updates their database on a daily basis with slight improvements, our services are currently updated every 6 months. For the most up-to-date version of the FEMA flood maps, please visit their National Flood Hazard Layer Viewer

Besides working with the layers in ArcGIS Online, you can also use the Copy Features tools in ArcGIS Pro and then run spatial analytics.

 

Do you have questions or comments about this blog? Post them in our GeoNet.

Also, thanks to Rich Nauman and Michael Dangermond on the Living Atlas team for developing this workflow and publishing the services.

About the author

Dan leads development of the Living Atlas of the World Environment content, which includes information about Earth's land, ocean, atmosphere, and ecosystems. Prior to Esri, Dan worked at NOAA for two decades, leading data visualization efforts for research, communications, and education.

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