Lecture0005

# Lecture0005 - Lecture 5. Geographic data Geographic data is...

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1 Lecture 5. Geographic data Geographic data is recorded information about the earth’s surface and the objects (features) found on it, associated to a geographic location. Model the earth and feature locations.

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2 Learning ArcGIS 9
3 Feature A representation of a real-world object on a map. Features can be represented in a GIS as vector data (points, lines, or polygons) or as cells in a raster data format. To be displayed in a GIS, features must have geometry and locational information.

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4 Extent and Resolution Extent is the range of minimum to maximum projected or geographic coordinates including all the features in the layer. Resolution is the projected or geographic dimension of individual features within the extent.
5 Vector Vector data model uses points, lines and polygons. The spatial data are the x,y coordinates for each point, line or polygon and attribute data is aspatial. Polygons represent things large enough to have boundaries (two dimensional). Lines represent things too narrow to be polygons (one dimensional). Points are used for things too small to be polygons (zero dimensional). x y points line polygon

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6 Vector data model Points are defined by a single x,y coordinate pair. Lines are defined by two or more x,y coordinate pairs. Polygons are defined by lines that close to form the polygon boundaries. x,y coordinates are pairs of values that represents the distance from an origin (0,0) along two axes, a horizontal axis (x) representing east-west, and a vertical axis (y) representing north-south. On a map, x,y coordinates are used to represent (model) features at the location they are found on the earth's curved surface. Every feature is assigned a unique numerical identifier, which is stored with the feature record in an attribute table. Vector-based systems are most appropriate for the study of cadastral (e.g., property boundaries) and political (e.g., county boundaries) data, which tends to have discrete boundaries.
7 Raster data model The raster data model uses row and column values to represent a map. Map position is related to position on the earth using the x,y coordinates of the upper left corner of the map (Price, 2004). Use for aspatial data that has a value for any particular location on the earth’s surface. Price, Maribeth. 2004. Mastering GIS. McGraw-Hill Companies, Boston, MA. 580 p.)

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8 Raster data model The earth is represented as a grid of equally sized cells. An individual cell represents a portion of the earth such as a square meter or a square mile. Only one x,y coordinate pair is normally use for each square area. This x,y coordinate pair (called the origin) is used to define the location of every cell. Each cell's location is defined in relation to the origin. Each raster cell is assigned a numeric value, which can represent any kind
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## This note was uploaded on 12/15/2010 for the course SAS SAS 18 taught by Professor Weswallender during the Spring '10 term at UC Davis.

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Lecture0005 - Lecture 5. Geographic data Geographic data is...

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