Content Comparison

Features

Most items within the Queensland’s Digital Topographic Data are known as features. Features are objects of the real-world with a spatial and geographical component.

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A derived dataset is a subset of a larger dataset. The purpose of these derived datasets is more efficient and focused datasets for specific needs e.g., emergency services for disaster management without the need to duplicate capture and maintenance in multiple datasets. They are also viewed/portrayed as a feature class.

Within the Digital Topographic Data, the following datasets are derived datasets:

• Community Facility Points

• Emergency Services Points

• Homesteads

• Shorelines

Feature Structure

In the vector data model, spatial features are represented as discrete geometric objects. These objects include points, lines, and polygons.

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Points - Defines point features or area features represented by a point that are displayed in mapping processes by a symbol. Multi-points that are two or more points that are treated as one feature are supported. Line/Polylines - A chain consisting of a sequence of non-intersecting line segments. A vertex is a change in direction along the length of a line segment or at the end of the line string. Multi-polylines are two or more polylines, not adjoining each other and treated as one feature.  Polygons - A bounded continuous region consisting of an interior area. Area-connected planar polygon with one external boundary are polygons that do not completely cover the interior area of the polygon. A void area within the polygon is not part of the same feature.  Multi-polygons are two or more polygons, not adjoining each other and treated as one feature. Multi-polygons can consist of polygons and holey polygons together.

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Table 1 - Feature geometry

• All polygon boundaries must be closed.

• Polygon features may contain an inner set of holes or voids that can be assigned to any feature class. For example, a Lake may have in the middle of it an area of dry land (terrestrial island).

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