Introduction to GIS

What is GIS?

• Stands for “Geographic Information System”

• For display and analysis of geographic information with computers

• Also known as “computer mapping”

Types of GIS Symbols

• Points

• Lines

• Polygons

• Images

• Towns, points of interest, campgrounds,…

• Rivers, roads, railroads,…

• States, countries, boroughs,…

• Satellite image, topographic map, shaded relief,…

Type Symbol Example

Image source: MapTEACH

Themes and Layers• GIS organizes information into layers

• Layers represent different “themes”

• A GIS map may have one or more layers

VegetationAirportsRiversVillages

Roads

Image source: MapTEACH

Example Thematic Maps

National Parks Sedimentary Basins

Museum Locations TopographyImage sources: http://www.nps.gov http://www.usgs.gov http://www.mapsofworld.com http://www.asgdc.state.ak.us/

How is GIS Used?

• Navigation• Emergency

response• Natural resource

management• Military• Business analysis• Education• And many more…

Image sources: http://www.dot.state.al.ushttp://www.cattlab.umd.edu

Why use a GIS?

• GIS maps are dynamic (can be changed). • Any information that has a location component

can be mapped.• A GIS anchors information to its real-world

location on a map.• We can display, measure, and compare

features.

From Sphere to Flat Map

• The Earth is a slightly squished sphere• We can describe any location with degrees of

Longitude: vertical lines W E of zero (prime meridian)Latitude: horizontal parallel lines N ↕ S of zero (equator)

• A globe is a model of the Earth

Image sources: http://sevencolors.org http://www.astro.columbia.edu http://www.eearthk.com

From Sphere to Flat Map• One simple way is to make a

grid of latitude and longitude.

• Then you can plot locations like x and y on graph paper.

• This is called the “geographic coordinate system.”

• The coordinate system is based on an approximation of the shape of the Earth (or “datum”).

• Since the Earth is irregular, the surface is changing (continental drift), and we have gotten better at measuring it.

• There are many “datums” to go with the geographic coordinate system.

• For Alaska, the most common datums are:– WGS84 (World Geodetic

System 1984)– NAD83 (North American

Datum 1983)– NAD27 (North American

Datum 1927)

Image source: MapTEACH

Why Make a Flat Map?

• The globe doesn’t fit in my desk drawer or my pocket.

• The globe doesn’t work very well for mapping detail.

• It is hard to measure distances and areas on a curved surface.

• So what do we do?

• Get the computer to “project” the map with mathematics.

Image source: http://www.kidsgeo.com and http://kartoweb.itc.nl

Which Projection?• There are many,many

projections to choose from.

• Most common types are:a. Cylindrical b. Conicc. Planard. Transverse Cylindrical

• Each projection distorts

• Your choice depends:– on the theme or purpose of

your map– the scale (large or small detail)– the location of the area on the

EarthImage source: http://www.NationalAtlas.gov

a.

b.

d.c.

Which Projection?• For Alaska, we use two basic types:

For Statewide small-scale data:“Albers Equal Area Conic - Alaska”

For Local large-scale data:“Universal Transverse Mercator” (UTM)

Image source: MapTEACH

Types of GIS Files

• Points

• Lines

• Polygons

• Images

• Towns, points of interest, campgrounds,…

• Rivers, roads, railroads,…

• States, countries, boroughs,…

• Satellite image, topographic map, shaded relief,…

Type Symbol Example

“Vectors”(shapefiles, .shp, .dbf, shx, …)

“Raster files or image files”(.jpg, .gif, .tif, .png, .bmp, …)

Image source: MapTEACH