1. Introduction to GIS

2. What is GIS? Geographic Information System Geographic implies of or pertaining to the surface of the earth Information implies knowledge of or collection of some form of data and finally, a system implies some form of organization, arrangement, etc.. Perhaps a framework?

3. ........ A computer system for capturing, managing, integrating, manipulating, analyzing and displaying data which is spatially referenced to the Earth." (R McDonnell & K Kemp. 1995. International GIS Dictionary. Cambridge: GeoInformation International)

4. GIS Components Overview Components: –Data –Maps/Views/Layouts –Spatial Analysis Physical Components –software –hardware –data –users –need/application

5. GIS Software Many types Around for > 30 years Only really prevalent for ~20 yrs? We will be using ArcView by ESRI Also ArcInfo by ESRI GIS software is loosely defined Some more applicable to certain tasks - ERDAS for example.

6. Hardware Software may dictate hardware in some cases - AWIPS! Generally: computer database printers and plotters, etc....

7. Data From many sources field collected spatial in nature point, line, polygons, grids METADATA!!!!!!!

8. Users Very wide range some users, some doers, etc... some want pictures some want answers some want to do analysis know your audience!

9. Applications What is the desired final product? Will the tasks be repeated over and over? Or is this a one time application?

10. What does a GIS do? Input data Manage data Manipulate data Perform analyses Produce output - maps, charts, a single number?

11. Let’s jump right to Arcview Organizes your data into a PROJECT A PROJECT contains: views, tables, charts, layouts, and scripts. Each of the above components also contians so-called components. Notice that I did not mention DATA!!!!!

12. Views Display themes or geographic data A view has an area for displaying the theme and an area for the “table of contents” - or what views are presently loaded.

14. Tables Display tabular data or the descriptive attributes of the elements in the data set.

16. Charts Display data graphically Different than the map type displays

18. Layouts The whole shebang?!?!?! Put it all together

19. Scripts Small computer programs Allow repeatability..... AVENUE

20. The Watershed A watershed is an area of land that drains to a single outlet and is separated from other watersheds by a divide. Hydrologic analysis and synthesis focus on the watershed.

21. The Watershed Every watershed has a drainage area. Related terms: drainage basin, sub-basin, sub-area.

22. Defining a Watershed Defining a watershed is generally referred to as delineating the watershed. The process involves determining that area within which water would drain to a common point. It is often easier to visualize the concept by pretending the ground surface is impermeable like cement.

23. Defining a Watershed Contours are lines of constant elevation. Contours “point” or “curve” uphill at stream crossings. Contours (generally) have constant spacing.

24. Defining a Watershed At right, the watershed has been delineated, using the contours, for the indicated watershed outlet. The streams/channel sections have also been highlighted within the watershed.

25. Defining a Watershed The most common form of mapping used for delineation are the USGS topographical maps. The most common map scale is the 7.5 minute 1:24,000 scale.

26. Defining a Watershed The use of electronic or digital data and mapping has become rather common place in the field of hydrology. GIS or Geographical Information Systems are used to manage, manipulate, and analyze digital data. One of the most common GIS data sets is a Digital Elevation Models or DEM’s.

27. Defining a Watershed This section is dedicated to providing a basic understanding of the methods used by a Geographical Information System (GIS) programs to delineate a watershed.

28. Defining a Watershed A GIS uses electronic data sets. The electronic data sets or coverages represent some property of the earth’s surface. One of the most common data sets is a Digital Elevation Model or DEM.

29. Defining a Watershed A DEM is used to represent the elevations of a section or area of land. The DEM is generally a gridded or raster data set. A raster data set means a series of rows and columns with each grid cell representing a property such as elevation.

30. Defining a Watershed Shown below (in 3-D) is a simple DEM, which is comprised of 12 rows and 12 columns.

31. Defining a Watershed In a plan view, the same DEM looks like :

32. Defining a Watershed The same DEM shown in an “interpolated” format:

33. Defining a Watershed The actual values of the grid cells in the rows and columns are illustrated in the table below:

34. Defining a Watershed In the DEM, each grid cell must be assigned a “flow direction”. It is the direction that the water would run or flow. One of the most common methods is the D8 algorithm. The D8 algorithm looks at 3x3 windows and assigns a flow direction to the cell in the center by considering the direction of the largest drop in elevation.

35. Defining a Watershed Consider the 3x3 group of cells below. The center cell flows or points in the direction indicated because that is the direction of the greatest elevation drop.

36. Defining a Watershed The flow direction is then assigned and recorded. In this example, the flow directions are simply 0 to 7 as shown below:

37. Defining a Watershed Each grid cell is assigned a flow direction. The resulting image of flow directions for the small 12x12 example is illustrated below:

38. Defining a Watershed Note that each grid cell flows into another grid cell and so forth. One could tally or keep track of the total number of grid cells that flow into each “downstream” grid cell. This is generally know as a flow accumulation data set. The flow accumulation data set for the 12x12 example is illustrated on the next page:

39. Defining a Watershed Flow accumulation data set