NR 422: GIS Review

Jim Graham

Fall 2010

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

Georeferenced Layers

http://jan.ucc.nau.edu/~rcb7/namNm15.jpg

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 Features (Shapes)

• Points

• Polylines

• Polygons

Topology

Wyoming

Colorado

Colorado

Wyoming

Non-topological

V1

V2

V4

V3

V1

V2V3

V4

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

Rasters (Digital Photos)

Zoomed In

Pixelation

Raster = Matrix of Pixels

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!