Post on 20-Dec-2015
transcript
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 GIS
1. Acquiring data
2. Preparing data
3. Assembling data (making electronic maps)
4. Analysis
5. 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!