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41 Cards in this Set
- Front
- Back
The first GIS was created in...
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1971
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Latitude
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measure how far north or south a location is from the equator
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Longitude
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measure of how far east or west a place is
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Mean Sea Level
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if the entire earth surface is covered by water. Have a single undisrupted global sea level covering the entire Earth which is adjusted to gravity. Also called the equipotential surface
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Geoid
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created by the MSL survace
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Elevation
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the vertical distance to the geoid surface
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Ellipsoid
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used to approximate the geoid surface
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Amount of flattening from spher to ellipsoid equation-
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F = 1 - b/a
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Ellipsoides are more commonly used than Geoids because-
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defined globally(mathematically simple)
-geoids are defined by geographically local conditions rather than single transfomration (computational demaning) |
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Datum
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if the entire earth surface is covered by water. Have a single undisrupted global sea level covering the entire Earth which is adjusted to gravity. Also called the equipotential surface
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Vertical Datum
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level surface to which heights are referred(geoid)
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Horizontal (or Geodetic) Datum
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a reference for horizontal poisiton (ellipsoid)(lat/long)
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Spheroid
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-will be used to transform the curvy earth surface to a flat paper map
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DMS to DD
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DD = deg + (min/60) + (sec/3600)
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DD to DMS
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D= int(DD)
M= int [(DD-D)*60] S {[(DD-D)*60]-M}*60 |
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Data Modeling
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process of abstraction form real world to representatioon in a GIS
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Levels of Abstraction
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-conceptual model-> data model ->data structures -> File structure
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Raster
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-Location based
-stores digital data in th eform of grid cells or pixels |
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Vector Data Model
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-Uses points lines and polygons to represent the world
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Topology
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-relationship among features
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Topological Space
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defined by the spatial relationships between geometrick elements
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Vector Topology
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- a collection of numeric data which clearly describes contiguity, containment, connectivity, and other topological relations between map features
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Why does topology matter?
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-store common boundary once
-store direction |
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Geographic Data Capture
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-the process by which data is taken from a specific source and entered into GIS
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Georeferencing
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-the process of adding real world coordinates to captured data
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% or more of the cost of most GIS projects is from
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building the database
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Primary Methods
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-process of recording geographic position and attributes from real world (surveying, GPS, remote sensor)
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Secondary Methods
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-the process of recording goegraphic position and attributes form abstracted sources (paper maps)
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Land Survey
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-primary method
-specifies boundaries and other legal descriptions by measuring point location on the earth's surface |
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Issues in the scanning process
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Physical size of the map
-level of detail needed -color or black and white |
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Issues in scannign represented as parameters
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-scanner dimension
-resolution -file format |
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Issues in the digitizing process
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-accuracy and precision
-Size of the digitizin gtable (map larger than table) -Operator accuracy, precision, and experience |
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Possible errors with digitizing
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-undershoots/overshoots
-open polygon |
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Georeferencing
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transform from image coordinates to map coordinates
-the process of relating coordinate in one space to another space |
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1st order polynomial transformation is an affine transformatioon that can...
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scale, skew, rotate, and translate data
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Root Mean Square Root
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= SQRT{Sumof all points(Re)^2)/n}
where Re= SQRT{(x1-x2)^2 + (y1-y2)^2} |
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Rectify
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Rotate and skew original image to match data points
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Query
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request for infomration
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Geographic dat contains two main parts
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-spatila features
-attribute information |
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Mandatory Files
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.shp- shape format
.shx- shape index .dbf- attributes in database format .prj- projection system |
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Optional Files
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.sbn and .sbx- spatial index of features
.atx- attibute index for .dbf .shp.xml- metadata in xml format |