Introduction to GIS

1. Introduction to GIS

2. What is GIS? • Stands for “Geographic Information System” • For display and analysis of geographic information with computers • Also known as “computer mapping”

3. Types of GIS Symbols Type Symbol Example • Points • Lines • Polygons • Images • Towns, points of interest, campgrounds,… • Rivers, roads, railroads,… • States, countries, boroughs,… • Satellite image, topographic map, shaded relief,… Image source: MapTEACH

4. Roads Villages Rivers Airports Vegetation Themes and Layers • GIS organizes information into layers • Layers represent different “themes” • A GIS map may have one or more layers Image source: MapTEACH

5. Sedimentary Basins National Parks Topography Museum Locations Example Thematic Maps Image sources: http://www.nps.gov http://www.usgs.gov http://www.mapsofworld.com http://www.asgdc.state.ak.us/

6. 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

7. 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.

8. 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

9. 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

10. 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

11. a. b. c. d. Which Projection? • There are many,many projections to choose from. • Most common types are: • Cylindrical • Conic • Planar • 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 Earth Image source: http://www.NationalAtlas.gov

12. 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

13. Types of GIS Files Type Symbol Example • Points • Lines • Polygons • Images “Vectors”(shapefiles, .shp, .dbf, shx, …) • Towns, points of interest, campgrounds,… • Rivers, roads, railroads,… • States, countries, boroughs,… • Satellite image, topographic map, shaded relief,… “Raster files or image files”(.jpg, .gif, .tif, .png, .bmp, …) Image source: MapTEACH