Geographic Information Systems Exam 1

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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