Geographical Information Systems

Transcription

1 Geographical Information Systems Geographical Information Systems (GIS) is a relatively new technology that is now prominent in the ecological sciences. This tool allows users to map geographic features of interest (similar to a paper map using a coordinate system). However, GIS databases also include attribute data associated with the geographic feature. For example, suppose one wants to map the locations of water samples taken along the Chippewa River. First, one would need to get the geographic coordinates for each sample using either an existing map or a global positioning system (GPS) receiver. The sample sites could then be mapped in coordinate space (longitude and latitude or metric units = Universal Traverse Mercator or UTM). Additionally, let s say one is testing these water samples for phosphorus (P) concentration. Each sample s P concentration could be entered into the GIS as attribute data. Other attribute data that could be entered might include: time, date, person collecting sample, weather conditions, etc GIS databases are valuable for mapping vegetation patterns, locations of animal populations, and for modeling changes in large-scale ecological patterns. GIS also is used in other fields including: law enforcement, land use and urban planning, and real estate. Although this technology has been around for over 20 years, individuals that are proficient using this tool are eagerly sought by employers. This lab will serve as a brief introduction to the use of GIS and related computer programs. Spatial data includes mapped information in a coordinate (X,Y) space. GIS databases allow this typical mapping ability, plus the addition of attribute data. Attribute data includes numeric or character information associated with a specific piece of spatial data. 1

2 Two data formats are used in GIS databases, raster data and vector data. Raster data maps information into grid cells or pixels that are defined by the user. For each pixel, spatial and attribute data are provided. Raster data is often used for very large data sets because computer processing time is faster. However, this data format is coarser in resolution of actual features on the ground. Vector data uses points, lines, and polygons to map information in a GIS. This data format is more accurate in mapping true features, however it is very labor intensive to collect and computer processing times are much longer compared to raster data. This figure shows a comparison between raster and vector data formats. The actual landscape features are noted in the map at the top. Note the use of polygons for the vector data format on the left lower panel. Note the pixels or grid cells for the raster data format on the right lower panel ) Which data format best approximates the real landscape? 2

3 Using ArcView: There are 2 primary GIS software programs used today, ArcView and ArcMap. Both are part of a larger computer package called ArcGIS. First, download all the ex1.* files off Gehring s Ecology web page under the GIS lab links. Save these into your My Documents space. There will be 5 total files. Open ArcView using the Start button and moving into the ESRI folder, then ArcView GIS 3.3 folder, and then to the ArcView GIS 3.3 file (see image to left). This screen will open at the start of ArcView. Choose OK for creating a new project with a new View. 3

4 The next screen will prompt you to add new data to the View. Choose Yes and navigate to the location of your ex1 files that you downloaded and saved. Maximize the View and ArcView GIS windows. Check the box in the Theme bar that comes up. This will display the data file (a shapefile). 4

5 This window should be displayed once you checked the box in the Theme bar. Now, double left click on the Theme bar. This will bring up the Legend Editor. Pull down the Legend Type menu and select Unique Value 5

6 Pull down the Values Field menu and select Habitat. Click Apply. Close the Legend Editor Window by clicking the X button. The View should now be redisplayed with different colors for the spatial landscape elements in the database. This map is a section of east-central Indiana. The different elements are indicated in the Theme bar of the View. 2) What data format is this? 6

7 3) What three (3) main landscape elements are found in this GIS database? Click on the Attribute Table shortcut button to display the attribute data in this database (note arrow). Attribute table for the Ex1 GIS database. 7

8 4) What attribute data is included in this GIS database? There are seven (7) habitat types identified in this database (fencerow, ditches, crop field, forest, grassland, human dwelling, and wetlands). 5) What is the most abundant habitat type? 8