nr 422: gis review
Post on 22-Feb-2016
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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?
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
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!
What can’t GIS do?• Guess the directions you want to take• Be 100% up to date• Be 100% accurate
Steps in GIS1. Acquiring data2. Preparing data3. Assembling data (making electronic
maps)4. Analysis5. Preparing final documents (inc.
Cartography)6. Distribution
GIS Process
Software- Preparation- Assembly- Analysis- Cartography
Spatial Data
Maps
Analysis Results
Input OutputManagement & Analysis
Preparation• Decompression (unzip)• File Format Conversion• Projection and Datum Conversion• Data Organization
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
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
Types of Data• “Discrete”• Vector • “Drawings”
– Points– Polylines– Polygons
• “Continuous”• Raster • “Photos”
– Grids
ESRI ArcMap Data Set GoogleMaps
• Cities (when at large extents)• Camping Sites• Starbucks!• Fire stations• Trees• Houses• Wells• Mines
Points
X1,Y1
X2,Y2
X3,Y3
Polyline (Network)• Streams• Roads• Pipelines
V1 (X1,Y1)
V2 (X2,Y2)
V3 (X3,Y3)
V5 (X5,Y5)
V4 (X4,Y4)
L1
L2
L3
L4
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
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
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
Vector Data Storage Options• ESRI / ArcMap Options:
– Shapefiles– GeoDatabases– Coverages
• GoogleEarth:– KML
• There are many others!
Shapefile• Most common throughout the GIS world• NOT Topological!• Files:
– “shp” – spatial data (coordinates)– “dbf” – attributes (dBase file)– “prj” – projection (includes datum)– etc.
Coverage• Was common
– Being replaced by Geodatabases?• Is topological• Contains files and folder
Geo-Referenced Raster• Known Projection and Datum
(X1,Y1)
(X2,Y2)
(X4,Y4)
(X3,Y3)
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
Geo-Referenced Raster File Formats• ESRI: Grids• GeoTIFF• ENVI: IMG• NASA: HDR• Many others!
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
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!
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
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!
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!
Defining the Reference System• ArcGIS Toolbox:
– Define Projection• Not
– Project!
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