The Road to Geocodes

GPS/GIS Builds County E9-1-1 Databases

by Bill Elliott

Photographs: (select thumbnail to view detail image)

Advanced GPS/GIS systems, such as the GeoLink® Field Mapping System, developed by GeoResearch, allow structures to be located with GPS at the same time road centerlines are being mapped. Used in a vehicle, GeoLink records the road centerline track while the operator maps roadside structure locations. Georesearch Putting it all together: With a program like GeoLink Powermap, Digital background maps can be used for navigation and reference purposes during field data collection. Georesearch

This article can be found on page 54 of the Nov/Dec 1998 issue of  9-1-1 Magazine.

As non-spatial, database-oriented Enhanced 9-1-1/Computer Aided Dispatch (CAD) systems come on-line at a record pace, another, less visible technology transformation is underway. Two newcomers, GIS and GPS, have awakened the industry to the inherent geospatial nature of E9-1-1 information. This realization, coupled with a fast approaching deadline for implementation of the FCC mandate requiring public safety call centers to provide wireless E9-1-1 service, will move GIS and GPS to the forefront of E9-1-1/CAD system implementations in the near future.

Rural Delivery and Public Safety

The majority of the U.S. population lives and works in urban or suburban communities. For the most part, buildings in populated areas are addressed sequentially by street blocks, odd numbers on one side of the street, even numbers on the other side. Most urban/suburban residents give little thought to this "municipal style" addressing system, assuming it is in place everywhere. In much of rural America, however, logical addressing systems do not exist, and in many areas, public roads have yet to be named and marked with signposts. Additionally, many rural homesteads have no assigned street address or visible address marker. Mail is typically delivered to a numbered mailbox on the side of a nearby public road with postal delivery routes meandering through the countryside from one numbered box to the next.

Postal route box numbers and unnamed roads offer little help in emergency situations when police or fire vehicles are dispatched to rural residences. The lack of posted road signs, logical street address schemes, and address markers, coupled with incomplete maps of structure locations, make implementation of effective E9-1-1 services in rural areas very difficult. Consequently, mapping and addressing projects have become a critical prerequisite to bringing E9-1-1/CAD systems on-line in rural counties.

Tabular MSAGs

A major component of an E9-1-1 call center is the Computer Aided Dispatch (CAD) system. CAD systems have traditionally been tabular in nature, but are increasingly becoming map-based as GIS and GPS tools are made available. E9-1-1 call centers receive the ANI/ALI information from the E9-1-1 equipment, pass it off to the CAD system where it is used to query a combined database commonly referred to as the MSAG or Master Street Address Guide. The purpose of the MSAG is to dispatch the responsible public safety entity to the caller's location based on the type of emergency reported and the caller's street address. MSAGs are created and kept updated in close coordination with the local telephone company and the U.S. Postal Service.

The MSAG tabular database is indexed by street names and address block ranges. It is used to identify which Emergency Service Zones (ESZs) serve the caller's area. An ESZ is a bounded area of responsibility served by a single fire, police or emergency medical district or station. Most often, each public safety entity (e.g. fire, police, and emergency medical) has its own uniquely bounded ESZs. Hence, residents served by a particular police precinct may not all be served by the same fire district. The MSAG contains Emergency Service Numbers (ESNs) that describe the unique combinations of emergency service agencies that serve a particular street address range.

Going Geospatial

E9-1-1/CAD databases, and particularly MSAGs, are inherently geospatial in nature. Structures are dispersed across a jurisdiction, and each structure's unique geographic location determines the form of the E9-1-1 response. This fact has not been widely recognized until recently when GIS software came into common use. The ability to map street block centerlines with address range attributes, geocode address locations to create structure nodes, and digitize Emergency Service Zone (ESZ) boundary polygons into a GIS, provides new capabilities for automating the creation and update of MSAG databases. Use of GIS spatial analysis tools, such as points-in-polygon, lines-in-polygon and polygon overlay can be used to full advantage for E9-1-1. Structures and street address blocks can be spatially related to ESZs (i.e. points-in-polygon, lines-in-polygon) while unique Emergency Service Numbers (ESNs) for address blocks can be automatically created using polygon overlay.

The advantages of using a GIS approach to MSAGs are quite stunning when one considers the time-consuming task of maintaining an MSAG as ESZ boundaries change and new streets, subdivisions and homes are built in a community. The movement of a single ESZ boundary line, adjusted perhaps to better allocate available resources, requires the regeneration of unique ESNs for every street address block in the effected area. This task can be automated using off-the-shelf GIS tools, compared to updating individual records manually in a tabular database. In fact, using a map-based E9-1-1/CAD approach (read: GIS), geospatial operators can be used to generate the majority of the reports and tabular databases needed for E9-1-1.

GPS/GIS as Database Builder

One of the major obstacles blocking early use of GIS for E9-1-1/CAD is the critical shortage of available geospatial data, particularly in rural counties. Since one goal of municipal style addressing schemes is to accommodate `fill-in' of address numbers as new structures are built, county addressing ordinances typically specify a unique, sequential street address every 10.56 feet on each side of the road (1,000 address number possibilities per mile, 500 to a side). Mapping structure locations (GIS nodes) at this accuracy requires map scales of 1" = 100' or 1" = 200'. Geographically referenced maps at these scales showing building locations are rarely available for rural areas.

GPS/GIS systems provide excellent capabilities for economically building E9-1-1/CAD maps in the field. These systems integrate GPS positioning, feature and attribute entry, and background reference maps in easy-to-use field system units that can be used both on foot and in a vehicle. Most GPS/GIS field mapping projects for E9-1-1 involve capturing GPS road centerlines, recording signed road names from sign posts, assigning IDs to unnamed roads, creating GPS location points for each structure, recording structure attributes, and noting visible structure addresses, if marked. GPS data is typically captured at +/- 1 to 2 meter accuracy to support the municipal style addressing schemes.

Readdressing Required

Once new road names and unique addressing anomalies are approved by county stakeholders, re-addressing is performed using software to assign each structure node a new address based on distance down the road in its address range block. In a typical scenario, readdressing efforts are approved at public hearings, new address notification letters are printed and mailed to residents, road signs are posted and address markers are placed on each property. Along with the E9-1-1 database, post office and telephone company records are updated with each new address.

Advanced GPS/GIS systems allow structures to be located with GPS at the same time road centerlines are being mapped. Used in a vehicle, such a system records the road centerline track while the operator maps roadside structure locations. Hot keys, data entry forms and pick lists support the rapid entry of road names, structure types, current addresses and other observed information in a format that can be loaded directly into a GIS. Digital background maps can be loaded and used for navigation and reference purposes during field data collection. Integrated laser rangefinders can be used to precisely measure offsets, and digital camera options support linking of structure photographs to each structure record. With all this capability, it is no surprise that GPS/GIS technology has quickly become the preferred method for creating the geospatial databases needed for E9-1-1/CAD.

The Wireless Nemesis

Most of the E9-1-1/CAD systems going "on-line" today are highly automated, yet tabular. When geospatial information is needed, incomplete and out-of-date paper wall maps and/or map atlas books are typically used. For many call centers, this approach is working satisfactorily. Why should an operational E9-1-1 call center with a tabular-oriented CAD system consider changing to a GIS-oriented system? This question can be answered in one word - wireless. The number of E9-1-1 calls made from cellular telephones is increasing exponentially. Studies and experience have shown that a significant percentage of wireless E9-1-1 callers cannot adequately describe to call takers the location of the emergency they are reporting.

Increasingly, a single traffic accident or roadside incident is being called into the E9-1-1 call center by several wireless callers, creating confusion as to which incident is being reported. As wireless providers begin to provide FCC-mandated E9-1-1 locational services, either with GPS or other technologies, E9-1-1 call centers will need to "map" wireless caller locations on computer screens in near real-time.

Map-based E9-1-1/CAD systems are ideally suited to support this requirement. Tabular systems do not provide capabilities to geocode incoming wireless caller coordinates in near real-time. GIS-based systems automate this function and display wireless caller locations on a digital map display. Once the wireless caller location is geocoded, the GIS can generate an ESN automatically through points-in-polygon operations. The FCC mandate has created a new awareness of the benefits of GIS, resulting in a flurry of activity in the development of GIS-based E9-1-1/CAD systems.

Toward Map-based Dispatch

The inherent geospatial nature of E9-1-1/CAD applications and the approaching deadline for locating wireless calls provide strong incentives for GIS and its supporting technology, GPS, to become the centerpiece of E9-1-1/CAD systems in the future. However, there is another potential advantage for adopting GIS on the dispatch side of the E9-1-1 equation. Accurate digital maps, created with GPS and used to locate E9-1-1 calls, will facilitate the real-time tracking of public safety vehicles as Automated Vehicle Location (AVL) technology is implemented in the fleet. By adding AVL capabilities to E9-1-1/CAD systems, dispatchers will be able to visually determine which response vehicle is closest to an emergency, track the dispatched vehicle as it moves toward the emergency, and verify its arrival at the incident site. The maturing technologies of GIS, GPS and AVL are poised to boost E9-1-1 and public safety applications to new levels of automation, efficiency and responsiveness in the future.