In this section, we'll take a closer look at two of the most extensive sources of publicly available roadway data: TIGER and OSM.
The TIGER database was first created in preparation for the 1990 decennial census. In creating TIGER, not only did the Census Bureau produce the first nationwide map of roadways, it also incorporated topographical context which defined the relationship between road features as indicated in its name: Topologically Integrated Geographic Encoding and Referencing database.
In addition to the TIGER spatial database, the Census Bureau also created a Master Address File (MAF) which is a database of all known living quarters in the U.S. The MAF contains about 300,000 addresses which are identified as location addresses, mailing addresses or both. In addition, the MAF contains a record for each living unit which can correspond to a separate structure or a residence within a shared structure. There are about 200,000 living units in the MAF some of which have multiple associated addresses. Following the 2000 decennial census, the Census Bureau decided to merge the two databases into a single database known as the MAF/TIGER Database (MTdb).
The Census Bureau is planning a 3-part informational series on TIGER to commemorate its 25th anniversary. Part 1 will examine the history of TIGER, Part 2 will address efforts to improve its accuracy, and Part 3 will address the tools which provide access to the data. To date, only Part 1 of the series has been made available. Spend a few minutes looking through the document to learn a little about TIGER’s history.
The TIGER data is available in a number of formats including Shapefiles, geodatabases, and KML files. The Census Bureau also provides a tool called TIGERweb which allow online viewing and the ability to incorporate TIGER data directly in GIS applications via web services including an OGC standard Web Mapping Service (WMS). For the exercises in this and the upcoming lesson, we will be working with the TIGER/Line shapefiles.
The Tiger/Line shapefiles are available for multiple years. Each year, the Census Bureau provides an updated set of Tiger/Line shapefiles in addition to associated technical documentation. The technical documentation for the 2017 Tiger/Line shapefiles can be found here. It is over 120 pages long and serves as an excellent reference for the Tiger/Line Shapefiles.
With more than 3 million registered users, the OSM project has a huge community behind it. Consequently, there is plenty of documentation available for learning about the project and becoming a member of the community. A few good resources for learning about OSM are the Open Street Map Wiki and the guides on LearnOSM.org.
OSM data is natively available in a unique file format (i.e., .osm files). However, many of the sites which provide access to OSM data serve it up in commonly used formats like shapefiles. For example, take a look at Geofabrik’s OSM data download page. Also, take a look at the first few sections of the OSM Data Guide which describe the .osm file format and some options for acquiring OSM data.
We often talk about spatial data in terms of points, lines, polygons, and attributes. OSM, however, uses the terms nodes, ways, relations and tags. In order to develop some understanding of these terms, take a look the descriptions of OSM data’s elements on the OSM Wiki site.