NR 422: GIS Review
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Transcript of NR 422: GIS Review
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What is GIS?• Geographic Information System?• Geographic Information Science?
• A system that provides the ability to work with information that is referenced to the surface of the earth.
• Is a paper map a GIS?
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What is GIS (con’d)?• A GIS contains at least:
– A Computer– A Software Application (ArcGIS)– Some Spatial Data– A User
• And works together to perform some geospatial function
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What can GIS do?• Make a map• Find directions to known location• Find local a Star Bucks• Determine cost of roads, developments• Predict the extent of an invasive species• Map ancient civilizations• Help manage natural resources!
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What can’t GIS do?• Guess the directions you want to take• Be 100% up to date• Be 100% accurate
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Steps in GIS1. Acquiring data2. Preparing data3. Assembling data (making electronic
maps)4. Analysis5. Preparing final documents (inc.
Cartography)6. Distribution
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GIS Process
Software- Preparation- Assembly- Analysis- Cartography
Spatial Data
Maps
Analysis Results
Input OutputManagement & Analysis
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Preparation• Decompression (unzip)• File Format Conversion• Projection and Datum Conversion• Data Organization
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Cartographic Elements• Minimal elements of a map:
– Title– One or more views of spatial data– Legend– Scale bar– Credits: Author and data sources– Projection and Datum– North Arrow
• Common elements:– Regional/Location map
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Layers and Attributes• Layer names with attributes:
– Cities: name, population– States: name, area– Parks: name, type– Plots: name, species – Trees: species, DBH
• Each city, state, park, plot or tree is a feature
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Types of Data• “Discrete”• Vector • “Drawings”
– Points– Polylines– Polygons
• “Continuous”• Raster • “Photos”
– Grids
ESRI ArcMap Data Set GoogleMaps
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• Cities (when at large extents)• Camping Sites• Starbucks!• Fire stations• Trees• Houses• Wells• Mines
Points
X1,Y1
X2,Y2
X3,Y3
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Polyline (Network)• Streams• Roads• Pipelines
V1 (X1,Y1)
V2 (X2,Y2)
V3 (X3,Y3)
V5 (X5,Y5)
V4 (X4,Y4)
L1
L2
L3
L4
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Polygons• Lakes• Political regions: Nations,
States/Provinces, Counties• Parks, Refuges, Forests• EcoRegions• Watersheds• Oil Fields
V1 (X1,Y1)
V2 (X2,Y2)
V3 (X3,Y3)
V4 (X4,Y4)
E3
E1
E2
E4
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Shapes• A Shape is one or more points, polylines,
or polygons that make up a geographic feature:– Stream network– Road network– Group of Islands– A park– A nation– A state– A county– A city
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Features• A single geographic element that can have
attributes attached to it:– River: Poudre River– Road: I-25– Islands: Hawaiian Islands– Park: Rocky Mountain National Park– Nation: United States– State: Colorado– County: Larimer– City: Fort Collins
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Vector Data Storage Options• ESRI / ArcMap Options:
– Shapefiles– GeoDatabases– Coverages
• GoogleEarth:– KML
• There are many others!
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Shapefile• Most common throughout the GIS world• NOT Topological!• Files:
– “shp” – spatial data (coordinates)– “dbf” – attributes (dBase file)– “prj” – projection (includes datum)– etc.
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Coverage• Was common
– Being replaced by Geodatabases?• Is topological• Contains files and folder
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Geo-Referenced Raster• Known Projection and Datum
(X1,Y1)
(X2,Y2)
(X4,Y4)
(X3,Y3)
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Types of Rasters• Aerial and Satellite Photos: Brightness• DEM: Elevation (meters)
– Slope: -90 to +90– Aspect: 0 to 360 degrees– Hill shade: Brightness based on sun angle
and slope • Topos: Brightness (RGB)• Indexes: Land Cover Type• Spatial Analysis: Varies
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Geo-Referenced Raster File Formats• ESRI: Grids• GeoTIFF• ENVI: IMG• NASA: HDR• Many others!
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Summary• Vector data:
– Points, Polylines, Polygons– Shapes and features– Topology– ESRI File Formats: Shapefiles, Coverages,
GeoDatabases• Raster data:
– Grids of rows, columns, cells– Cells contain pixels– Pixels can have one or more samples– ESRI File Format: Grid– Types: Photos, DEMs, Topos, Land Cover Type
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Where are we?• If you’re at:
– Coordinate: 450321, 4124324 – Where are you?
• Can’t tell without a system to “reference” the coordinates to the earth, we are lost!
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Coordinate Reference Systems• Units:
– Degrees, Feet, Meters, Miles, Kilometers• Coordinate System
– Cartesian or Rectangular– Spherical
• Projection– Geographic or Un-projected– UTM– State Plane
• Datums:– NAD27, NAD83, WGS84, HARN
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Coordinate Reference Systems
• Bottom Line:– The projection, datum, and units must be
defined for data to be referenced together– The projection, datum, and units must be
the same for detailed analysis
• For now:– Make sure each of your files has a
projection and datum defined!
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Finding the Reference System• All of these are reference systems:
– ArcCatalog: – ArcMap Layer Properties:– ArcMap Toolbox: “Projection”– “prj” file
• If it’s not there:– Check the metadata (xml file)– Check the web site– Contact the provider!
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Defining the Reference System• ArcGIS Toolbox:
– Define Projection• Not
– Project!