How to find an area with GIS

by Marcela I. Diaz [150715 10:15]


   Using USGS to find elevation infomation


  1. Go to USGS web page: www.usgs.gov

  2. Click on Maps, Imagery and Publications tab.

  3. From the Maps and Data optionson te right hand of the secreen choose National Map>.

  4. Click on FindData + View and Download.

  5. Click on "here".

  6. Input given point coordinates or write place name (i.e."tierra del sol") > Search.

  7. Zoom into desired area.

  8. Click the Download data icon (below the Annotation tab) > click on here to draw and download by a bounding box.

  9. Box desired area

  10. Choose Elevation DEM Products > Next

  11. Select 1 Arc-second Arc Grid

  12. Download Selected Product

  13. Save

  14. Open New Folder on Desktop

  15. Save downloaded file in new folder

  16. Unzip downloaded file



   Using GIS to find a watershed area


  1. Open ArcMap and a new blank map.

    • Do not open an existing map file. Remember to save your work frequently. Save map (.mxd).

  2. Load you DEM into ArcMap

    • Go to File > Add Data> Add Data, select your DEM folder (Upper left). If asked to build pyramids say Yes.

  3. Turn on Spatial Analysis toolset

    • Click Customize > Extensions > CHECK Spatial Analyst > Close.

  4. Create a Depressionless DEM

    • Open ArcToolbox > Spatial Analyst Tools > Hydrology > Fill.

    • In Input Box, choose file.

    • In Output Box, name new file for fill (Example: tds_fill) > OK.

    • Remove the original (not the fill).

  5. Create Flow Direction Raster

    • Arctoolbox > Spatial Analyst tools > Flow Direction.

    •  In Input box, choose fill file.

    •  In Output box name new flow direction file (Example: tds_fd) > OK.

  6. Create Flow Accumulation Raster

    • ArcToolbox > Spatial Analyst tools > Hydrology > Flow Accumulation.

    • In Input box choose Flow Direction Raster file

    • In Output Box Name new Flow Accumulation Rater File (Example tds_fa).

    • Right click on Flow Accumulation Layer > Porperties > Classified > Change to 2 classes > Classify > Break Values. Change first value to 1000 > OK

    • Choose no color for symbol 0-1000.

    • Choose any other color for the second classification.

    • Apply

  7. Create Watershed pour point

    • Click on XY icon.

    • Input Coordinates (long, lat)

    • Select the point icon (circle with point).

    • Zoom in to point and make sure the pour point is within a flow pixel, if not, then move manually (click on arrow icon, move point, make sure to save file).

    • Right click on Layers icon > Convert Graphics to features> Output Shapefiles > Data Frame.

    • Make sure you are in right folder, name Outlet Folder (Example: tds_out).

    • Click on Shape File > YES.

  8. Delineate Watershed

    • Open ArcToolbox . Spatial Analysis Tools . Hydrology > Watershed.

    • In Input box select Flow Direction File.

    • Select the shapefile of your pour point as the input raster or feature point data.

    • Accept the other defaults and navigate to your folder you have been working in and name the output surface raster (Example: tds_delin) > OK.

    • The new watershed raster will be added to the data frame. You may have to zoom in to see it all.

    • Convert the watershed raster to a polygon shapefile for use later (ArcToolbox > Conversion> Tools > From Raster > Rater to Polygon).

    • Input Raster should be your watershed delineation > Output to working folder and save as tds_ws.

    • Once the _ws shapefile is finished and in your table of contents, you can double-click the Colored box > Hollow > Outline > Width 2 > Outline Color: Black.

  9. Load Topo Basemap

    • File > Add Data> Add Basemap > Topographic.

    • Uncheck your DEM, Flow Direction, Watershed Delineation, and Flow Accumulation layers if you want to view just the basemap and your watershed outline.

  10. Watershed Area

    • Change Coordinate System to UTM (meters)

    • Right click on Layers icon in the table of contents and select Properties.

    • Select the Coordinate System > find Projected Coordinate Systems > UTM > WGS 1984 > Northern Hemisphere > WGS 1984 UTM Zone 11N > OK.

    • Right click on your tds _ws shapefile > Open Attribute Table > Click the table options dropdown menu . Add Filed > Name: Area mi2 > Type: Long integer > Leave Field Properties as default > Click OK.

    • There now should be a new column in your attribute table titled Area mi2. Right click the Column > Calculate Geometry> Property: Area > Leave Coordinate System as default > Units: Square Miles US [sq mi] > Click OK.