![]() ![]() “A Classification of Software Components Commonly Used in Geographic Information Systems.” In Proceedings of the U.S.-Australia Workshop on the Design and Implementation of Computer-Based Geographic Information Systems, 70–91. The simplest vector data structure is called the spaghetti data model (Dangermond 1982).Dangermond, J. We will examine two of the more common data structures here. Vector data models can be structured many different ways. Polygons have the properties of area and perimeter. Polygons are used to represent features such as city boundaries, geologic formations, lakes, soil associations, vegetation communities, and so forth. In the case of polygons, the first coordinate pair (point) on the first line segment is the same as the last coordinate pair on the last line segment. Polygons are two-dimensional features created by multiple lines that loop back to create a “closed” feature. Lines that directly connect two nodes are sometimes referred to as chains, edges, segments, or arcs. Lines are used to represent linear features such as roads, streams, faults, boundaries, and so forth. Lines are one-dimensional features composed of multiple, explicitly connected points. Points can be spatially linked to form more complex features. Vertices are defined as each bend along a line or polygon feature that is not the intersection of lines or polygons. Specifically, a point is a stand-alone feature, while a node is a topological junction representing a common X, Y coordinate pair between intersecting lines and/or polygons. Other types of point features include the node and the vertex. Points have only the property of location. Points are typically used to model singular, discrete features such as buildings, wells, power poles, sample locations, and so forth. ![]() Points are zero-dimensional objects that contain only a single coordinate pair. ![]() Three fundamental vector types exist in geographic information systems (GISs): points, lines, and polygons (Figure 4.8). The spatial information and the attribute information for these models are linked via a simple identification number that is given to each feature in a map. The data attributes of these features are then stored in a separate database management system. Geographic Information Systems: A Management Perspective. Vector data models use points and their associated X, Y coordinate pairs to represent the vertices of spatial features, much as if they were being drawn on a map by hand (Aronoff 1989).Aronoff, S. In this model, space is not quantized into discrete grid cells like the raster model. In contrast to the raster data model is the vector data model.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |