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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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One-Dimensional Entities in a Two-Dimensional Field: Lines

You saw examples of lines representing streams and sewers in Chapter 1. Lines were also used there to delineate boundaries of polygons. A line may be used to represent a linear feature that is too narrow to have a meaningful area. As with zero-dimensional entities, vertices on a line may have a “z” (e.g., altitude) value.

In GIS Terms, a line is a simple geometric entity that consists of a sequence (that is, an ordered set) of vertices, which are simply coordinate pairs or triples. Between each adjacent pair of vertices there is a segment. A segment is frequently simply a straight line, but in vector-based geodatabase feature classes, it can also be a part of a circle or ellipse, or it may be a spline (called a Bézier7 curve). A line that consists of multiple straight-line segments connected at vertices can approximate a curve. Lines can therefore be used to represent curvilinear features, such as roads and streams. The segments of a line are not allowed to intersect each other.

Paths—A path is a line as described previously, composed of a sequence of connected segments (or a single segment). The term “path” is used in vector-based geodatabase feature classes.

Polyline—A polyline is made up of one or more paths. If there are multiple paths, the paths may be connected or disjoint. Even if a polyline representing a feature consists of multiple paths, it has only one row in the attribute table. If polylines are used in shapefiles, ...

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