Linear Features

Andrew Flora

Geographer

Linear Features Branch

Geography Division

US Census Bureau

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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.

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Spatial Primitives

• The basic topological building blocks

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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

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Spatial Primitives

• Edges are flagged as belonging to one or more specific feature classes (or no feature class).

• - Roads• - Rail• - Hydrography• - Other linear feature

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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.)

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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 S16301. S - Defines the Super Class “Roads”2. S1630 - Defines the specific class “Ramp”

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Features

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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.

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Feature Models for Roads and Hydrography

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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….

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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).

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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.

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Building a Road Feature

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Road Features

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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

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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.

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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.

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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.

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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.

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Questions