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Linear Features

Linear Features

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Linear Features

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  1. Linear Features Andrew Flora Geographer Linear Features Branch Geography Division US Census Bureau

  2. Basic Building Blocks • Nodes, Edges, and Faces form the basic topological primitives or building blocks for the MTDB. • Features build on topological primitives to define real world geography. • Definitions, data Models, rules, and legal values define the types of data and features in the database and the relationships between the features. • Update processes update and edit the data.

  3. Spatial Primitives • The basic topological building blocks

  4. Spatial Primitives • “Connected” nodes define edges that are vectors with a from- and to-direction and a left- and right- side. • Connected edges form faces. • Point features are associated to “Isolated” and “connected” nodes. • Linear features are associated to edges • Area features are associated faces

  5. Spatial Primitives • Edges are flagged as belonging to one or more specific feature classes (or no feature class). • - Roads • - Rail • - Hydrography • - Other linear feature

  6. Features • Features use the topological primitives to define real world objects. • Features include visible geography such as roads, rivers, fences, pipelines, and rail lines) • Features include nonvisible geography such as property lines, ferry crossings, and extensions • (An edge is not anything in the MTDB unless it is a feature.)

  7. Features • Features must be either points, lines, or areas. • Composite features can incorporate features with different geometry but share a common attribute such as name. (planned but not developed in the MTDB). • Minimally all features must have a MAF/TIGER Feature Classification Code (MTFCC) for example S1630 • S - Defines the Super Class “Roads” • S1630 - Defines the specific class “Ramp”

  8. Features

  9. Multi Layer Features • Different Linear features can share the same edge geography. • Business Rules restrict the types of features can occupy the same locations: - Two roads can share an edge; - A road and a rail feature can share an edge; but - An edge cannot be a road and a river. - An edge can be a boundary and a road or other type of feature.

  10. Feature Models for Roads and Hydrography

  11. Building a Road Feature • The MTDB models all road features as street centerlines. • Divided road features may have two street centerlines separated by a median face. (Separate features identify each of the separated roadways) • Some of the features included are: - S1100 Primary road - S1200 Secondary road - S1400 Local neighborhood road, rural road, city street - S1500 Vehicular trails (4WD) - S1630 Ramp - S1640 Service Drive - ….etc….

  12. Building a Road Feature • A road feature consists of a series of connected edges that share the same MTFCC, feature name, and a limited number of related attributes. • All road features must consist of “road” edges. • Attributes describing the road are divided up into edge, road edge, and feature attributes. (the goal is bring as many edges as possible into a single feature and while maintaining attributes restricted to a part of the feature, such as paving type or number of lanes, to the edge).

  13. Building a Road Feature • Each road name associated with a road becomes a separate MTDB feature. • Separate features share all or part of the same sets of edges to express the full inventory of feature names. • Each feature that shares an edge has the same MTFCCs. • All road edges must belong to a road feature. • Unnamed roads have unnamed features, but must have an MTFCC.

  14. Building a Road Feature

  15. Road Features

  16. Hydrographic Features • May have an area or linear representation, (or a combination of both). • Include such features as: - H3010 Stream river - H3013 Braided stream - H3020 Canal, Ditch, or Aqueduct - H2030 Lake/pond - H2040 Reservoir - H2041 Treatment pond - H2051 Bay/Estuary/gulf/sound - H2053 Ocean - H2060 Gravel Pit/Quary filled with water

  17. Linear Hydrographic Features • The MTDB maintains single-line features for streams, rivers and canals. • Features follow the feature centerline. • Linear features can share all or some of the same edges to represent alternative names (like roads) • Attributes such as “persistence” are maintained on the hydro edge.

  18. Area Hydrographic Features • Area features consist of water faces bounded by a non-feature edge shoreline. (the water body is the feature) • Area features can share all or some of the same faces to represent alternative names or specific names for parts of the feature such as a bay in a lake. • All features that share the same set of faces must have the same MTFCC.

  19. Area Hydrographic Features • Artificial Paths (Census defined or NHD) extend through area water : - they provide a linear representation of streams that run through lakes and ponds. - They serve to connect linear hydro features that enter lakes and ponds. • Boundaries can follow shoreline edges, artificial paths, or other edges that appear in water.

  20. Restrictions and Edits • Detailed data models and operational definitions are necessary to ensure consistent results. • The structure of the database limits the structure of features. • Business rules restrict relationships 1) Restricts the types of features can share the same geometry 2) Restricts the types of attributes on a feature. • Edits are needed to ensure updates are compliant with data models and business rules.

  21. Questions