MCP Insights

With GIS Centerlines, the Devil Often is in the Details

Posted on August 12, 2020 by Glenn Bischoff

Public safety agencies draw polygons using their geographic information systems (GIS) that define their jurisdictional footprints and the areas in which they provision emergency services. When such polygons abut, generally along jurisdictional borders, they must “snap” to each other; another way of expressing that is to say that the polygon borders must be coincident. If they are not, overlaps and/or gaps can occur—both are problematic from an emergency response perspective. Jurisdictional boundaries most often are in the form of road centerlines, which represent the center of a real-world road.

If an emergency call is placed in an overlap or gap area between two adjacent jurisdictions, data associated with that call will not be accepted by the emergency services Internet Protocol network, or ESInet, which is the platform that transports the call to the correct emergency communications center (ECC)—also known as a public safety answering point—in a Next Generation 911 (NG911) environment. When that happens, the ESInet won’t know which ECC should receive the call. So, the call will default-route to the center that is defined in the state’s routing policy.

The chances are very high that the answering PSAP will not be the correct PSAP. When that happens, the call then has to be transferred to the correct ECC, a process that usually takes seconds but can take minutes—which is an enormous amount of time when lives are on the line.

Sometimes adjustments have to be coordinated with neighboring jurisdictions, based on unique nuances. One such situation involved the Monocacy River, which provides the border with Frederick County. Typically, the river’s centerline would be drawn at the midpoint between the two shorelines. But in this case, Carroll County, located in Maryland, is responsible for all water rescues on the river.

So, the line had to be moved to the Frederick County shoreline—if it hadn’t been moved, any calls involving emergencies on the Frederick County side of the river that required a water rescue automatically would have routed to Frederick, which then would have to transfer the call to Carroll County—again wasting precious time.

In the case of Carroll County, Mission Critical Partners was working on a project to support the County's GIS and NG911 goals, and as part of that project, was coordinating GIS data development and maintenance and coordinating with neighboring jurisdictions to validate agreement between each entity's road centerlines, PSAP boundaries and provisioning boundaries.

MCP’s expertise paid huge dividends in this regard, according to Tom Dowd, GIS division manager within the county’s Bureau of Technology Services.

“MCP was able to help both sides work through processes and resolve issues,” he said.

Read more about this project in our case study, "MCP Helps Carroll County Move Closer to NG911 by Supporting Its GIS Mapping Efforts."

Resolving issues is one of the things we at MCP do best. If you have any issues regarding your migration to NG911, particularly as they relate to GIS, or simply would like to receive some expert advice, please reach out.

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