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Lecture 13, 14

Terms in this set (18)

data input
transfer data into the GIS from external sources; must allow for encoding in either raster or vector; must provide a means for spatial referencing (projections and coordinate systems etc.); must provide link between storage and editing subsystems (ensure input can be saved and errors corrected)
raster data input
source images and maps have different projections and scales, so data transformations may be needed t bring all the data to a common coordinate system
importing digital image
method of raster data input; importing or loading digital images into geodatabase; you can store many raster datasets in a geodatabase, or mosaic all your rasters into a single raster dataset
scanner for digital graphics
method of raster data input; converting existing maps (hardcopy) to digital form; a scanner is connected to a computer and map features are scanned automatically
(different size scanners: A4, A3, A2, A0) (different accuracy/resolution: 300, 600, or 1200 dpi)
rasterization
method of raster data input; ArcGIS allows conversion of vector features into raster using different algorithms; first, superimpose a grid on the vector map... then, assign a value for the cells based on the contained feature
vector data input
features are encoded as coordinates on a particular coordinate system, and must have the same coordinate system as the base map; data transformation may be needed to bring all data to a common coordinate system
vectorization
method of vector data input; ArcGIS algorithm to convert raster into vector; resolution (or cell size) has a direct effect on the spatial integrity of the object; lines become block and step like, so you must apply a smoothing function to vector lines
grid overlay
method of vector data input; and old method that is seldom used; grid of clear material is overlaid on a map, and the identity of each cell in the grid is determined by what map features are in a particular cell; a number or code is assigned to each class of map features, and used to label cells in the grid
digitization
method of vector data input; the process of converting existing maps to digital form; features are traced manually; can be down by using digitizing table connected to computer, or screen digitizing using mouse
digitizing table
used to digitize hard copy maps into GIS; transforms wire intersections into coordinates of the tablet's coordinate system; the tablet is composed of a flat surface, in which are embedded a grid of electronically active wires and mouse-like devices (puck) usually with cross hairs
-when puck is moved over the tablet, its location is known because the grid of wires senses its location
-Grid acts like a cartesian (x,y) coordinate system
snapping tool
allows you to create features that connect to each other so your edits are more accurate, with fewer errors; when it is turned on, your pointer will jump to edges, vertices, and other geometric elements when your pointer is near them within a certain tolerance; enables you to position a feature easily in relation to the locations of other features
trace tool
in edit toolbar; traces feature boundaries; good for complicated shapes
smooth tool
smooths sharp angles in polygon outlines to improve aesthetic or cartographic quality
cut polygons
creates two polygons from one original; a new record will be added to attribute table for the new polygon
merge polygons
creates one polygon from two original; only one record in the attribute table for the new polygon
union polygons
creates a new coverage by overlaying two polygon coverages; the output coverage contains the combined polygons and attributes of both coverages
edge matching
aligns features along the edge of one layer to features of an adjoining layer; the layer with the less accurate feature is adjusted, while the adjoining layer is used as the control
spatial adjustment
GIS data comes from different sources, so geometric distortions may be introduced by imperfect registration in map compilation and a lack of geodetic control in source data; this corrects flaws through the geometric adjustment of coordinates
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