Nationwide Navigation Comes to GIS

In the fall of 1998, Geographic Data Technology, Inc. (GDT), an Esri Business Partner, embarked on a project to enable detailed navigation on its nationwide street database products. GDT's street network products have long supported geocoding and traditional Business geographic applications, but the addition of a number of navigation attributes now enables the products to support such demanding applications as fleet management, tracking, logistics, location-based services, and, most recently, in-car navigation. Using its time-proven compilation approach to database building, GDT's transition into nationwide navigation has been efficient, with a high level of involvement from key customers within these new markets.

Core to GDT's database building methodology is the belief that by serving the needs of dozens of distinct markets within a single database, each separate application and market benefits from the accumulated feedback of other applications, both within the same market and in different markets that may share common needs. The vast majority of GIS applications share many common data requirements regardless of market or geographic focus. Most users want GIS data to

• Be able to spatially locate entities based on various known attributes (or, in traditional GIS terminology, to geocode).
• "Look like a map," meaning that water bodies, golf courses, and other landmarks are necessary reference features.
• Behave like the real world. Just knowing that a feature is a street isn't always enough information. Is it one-way? Is it a limited access highway? Is it a toll road? Streets have different characteristics, and often they result in different decisions within an application.
• Interact like the real world. If it's a highway, does it meet the cross street at grade? Is a right turn legal at this particular intersection? Again, different types of streets interact differently with one another, and many applications depend on knowing and understanding those interactions.

Meeting these shared requirements nationwide requires an understanding both of geographic commonalities and distinctions. For example, the borough of Queens, New York, has unusual addressing wherein the address contains a hyphen (123-05 116th Ave.). Salt Lake City, Utah, street signs use a different naming standard than the United States Postal Service for the same streets. In many urban areas in Michigan, a left turn of a street with a median requires driving through the intersection, making a U-turn on a dedicated passage through the median, then making a right turn toward your destination (a "Michigan U-turn"). The list of exceptions is endless, yet in most cases they are not truly unique. Addresses in Hawaii also contain hyphens, so the ability to understand a Queens, New York, addressing scheme helps clarify Hawaiian addressing schemes. And, in fact, most cities contain maneuvers topologically equivalent to a Michigan U-turn although the exact implementation may vary slightly. Every new situation benefits from lessons learned in other areas.

To maintain a database with this level of detail, containing more than 6.2 million miles of streets in the United States (and more than 500,000 miles in Canada), GDT works with more than 45,000 contacts to compile national data with local understanding. Working with Esri and its ArcIMS software, GDT has recently expanded its contact with municipal and regional government agencies via the Community Update program. Community Update couples GDT's GIS database management expertise with the knowledge of agencies dedicated to defined regions. Under the Community Update structure, municipal and regional government agencies use an Internet-based system to send new and updated information about local streets to GDT, where the information is validated, cross-referenced, and integrated with other data before being returned to a local server for downloading by the participating agencies. By sharing the benefits of a compiled database, participants are able to share in the creation of a consistent nationwide spatial data infrastructure while still serving the needs of their local communities.

During the past two years, GDT has significantly increased the list of information gathered from its wide range of contacts—both traditional information sources and Community Update participants. The street attribution that GDT compiles and delivers has expanded to include Z levels (showing overpass/underpass relationships), turn restrictions/maneuvers (delivered as turntables in ArcInfo or ArcView GIS), one-way directionality, average traversal time, Artery Classification Coding (ACC), and highway shield information in addition to all the addressing and naming fields. Street names are now flagged to indicate the best name for geocoding and the best name for most routing itineraries. Many of these navigational elements are concentrated in areas with dense and complex networks. Recognizing this, GDT's efforts radiate from metropolitan areas as well as from the all-important national highway system.

Just as important as the navigation attributes and relationships stored in a database is the geometric network that they are tied to. GDT is in the process of aligning and verifying the positioning of all geometry to meet or exceed the requirements of the navigation industry. Using the National Standard for Spatial Data Accuracy (NSSDA) guidelines for measurement, the vector data is being aligned to raster imagery, existing vector sources, and GPS data. Incoming data sources undergo rigorous testing to ensure that they meet currency and accuracy requirements. This includes an ever-growing database of established, field-verified, DGPS control points. Most edits are now made with the aid of one-meter imagery in the background, providing valuable information such as Z level as well as an overall understanding of what happens in real life. This translates into a direct user benefit by ensuring that data looks, behaves, and interacts like the real world.

For an Esri software user, all of GDT's data improvements are immediately accessible in ArcInfo, ArcView GIS, or ArcSDE. Dynamap/Transportation Data is optimized specially for each format, taking advantage of the built-in capabilities of each package. An ArcView GIS user, for example, can load the data and generate routes immediately. One-way streets, Z levels, and other attributes will be recognized and accounted for by ArcView Network Analyst without further processing. Geo-coding is fully supported out-of-the-box, including full access to alternate street names in a single pass. ArcSDE users benefit from a robust, easy-to-use data loader, which preverifies geometry and supports transactional updates. GDT delivers hundreds of ArcSDE formatted shipments every year for applications across North America. In addition, GDT is a member of Esri's UNETRANS Consortium, which is creating easily implemented data models.

For more information, contact John Cassidy, GDT (tel.: 1-800-331-7881, ext. 1115).

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