Roads, Highways, Railroads
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TIGER Edge File Shapefile
In the context of U.S. Census Bureau geography, "TIGER Edges" refers to the linear features within the TIGER/Line files. This is a fundamental concept in the topological data model used by the Census Bureau.
What are Edges in TIGER?
In a topological data structure, a map is made up of three basic primitives:
| • | Nodes: The endpoints where lines (edges) meet. |
| • | Edges: The lines themselves, which represent features like streets, rivers, or railroads. |
| • | Faces: The polygons that are bounded by the edges. These represent areas, such as census tracts, counties, or lakes. |
TIGER Edges are the linear primitives that connect nodes and define the boundaries of faces. They are the core of the TIGER/Line data that describes features on the ground.
Characteristics of TIGER Edges
| • | Linear Features: The most common and useful type of TIGER edge is a street or road. They also include railroads, power lines, and hydrography (rivers and streams). |
| • | Address Ranges: For street edges, the TIGER data includes "address ranges." This means that for each side of a street segment, the file contains the starting and ending house numbers. This is a crucial attribute that allows for geocoding—the process of converting a street address into a geographic coordinate (latitude and longitude). |
| • | Topology: The term "TIGER" itself stands for Topologically Integrated Geographic Encoding and Referencing. The "topologically integrated" part means that the edges are connected in a way that avoids gaps and overlaps. This ensures that a county boundary, for instance, is perfectly aligned with the roads and rivers that define it. This makes the data incredibly useful for analysis, as you can trust that features are spatially coherent. |
| • | Metadata: The TIGER/Line files for edges also contain a wealth of metadata. This includes unique identifiers, street names (both primary and alternate names), feature codes that classify the type of edge, and information about the left and right "faces" (the geographic areas on either side of the edge). |
The "All Lines" or "Edges" Shapefile
When you download TIGER/Line files, the linear features are typically found in a shapefile named something like tl_2024_us_edges.zip or tl_2024_xx_edges.zip (where xx is the state FIPS code). This is the file you would use for mapping road networks, geocoding addresses, or performing network analysis.
In summary, TIGER Edges are the foundational linear components of the Census Bureau's geographic data. They are a critical part of the TIGER system's topology and are essential for everything from creating a basic map of a city to advanced spatial analysis and geocoding.