Working with Land Use/Satellite imagery

Hands-On Exercise Notes

6/10/2002

Objective:

Help participants explore and use remotely sensed land use/land cover data and satellite data sets, in combination with other GIS data to solve problems.

Resources:

Handout of step-by-step notes, land use data CD (to request a CD send email to: dath.mita@ndsu.nodak.edu or phone: 701 231 6551) ArcView 3.x GIS software, ArcView optional extensions Image Analysis and Spatial Analyst.

q Displaying and Analyzing land use imagery:

q Using Standard ArcView environment

1. Start ArcView GIS from Windows Start, Programs, ESRI, ArcView 3.x and cancel the welcome window.

2. Open a New View in the project window and insert Land Use CD in the appropriate drive (maximize the application window and move the view to top right corner).

3. Set the working directory from the file menu to C:\window\temp or to a directory of your choice.

4. Click Add Theme from the View Menu.

5. Navigate to the CD-ROM drive with the Land Use CD.

6. Under Data Source Types scroll down and select Image Data Source

7. Double click on the Project Folder.

8. Select a file with a .gis extension (image file in ERDAS Imagine data format).

9. Click OK to add the image file to the view.

10. Open View properties to rename the view window “Std Arcview”, also change the background color to any color of your choice (click Select Color in the dialog).

11. Open the Theme Properties and rename the theme e.g. “2000 Land Cover”.

12. Check the box next to the theme name in the view’s Table of Contents (TOC) to display the theme in the view window.

13. Does the TOC contain a legend for the image? Notice also that the Open Theme Table button is disabled (under the Theme Menu), why is that so? Open the Legend Editor from the Theme menu and click on Colormap

14. Can you use the Identify tool to query image pixel information?

15. Overlay or add County Boundaries layer to the view by Add Theme and select Feature Data Type and choose Nd-cty.shp file. Change the theme symbol to transparent (open legend editor + click on the symbol + X box). Rename the theme to County Boundary. Display the theme in the view (this is projected vector data set). You may label the counties.

q Using Image Analysis Extension to extend ArcView 3.x to support image display, creation, and analytical processing.

1. Go to File Menu and select Extensions.

2. Under Available extensions scroll down and check the box next to Image Analysis.

3. Click OK to load the extension into the GUI, when loaded the Menu interface has an additional Image Analysis Menu as well as Align Tool, Seed Tool, etc.

4. Go to View Menu and Add Theme and select Image Analysis Data Source as a data source type and choose one of the image files with .gis extension (if asked to calculate pyramids click yes?)

5. Does the TOC contain a legend for the image? Notice also that the Open Theme Table button is disabled (make sure the theme is active), why is that so?

6. Open legend editor (double clicking the theme name in the legend) to edit/modify the legend, delete the zero counts categories (do not delete the “0” value row): select symbol and delete using the X-button and click Apply (check what options are under Values Field). Change the zero value symbol to a different color.

7. Save the new legend for future use (legend.avl) with Image Analysis theme of the same kind. Close the legend editor

8. Make the new Theme active and go to Edit and click Copy. Open a new View from the project window and paste. Rename the View “Image Analysis” and display the theme into the view.

9. Compare the tools made available in the menu display for the two views. Also compare the image Theme Properties (image definition, information etc). Which theme gives more information?

10. Use the Identify tool to query image pixel information (zoom in closer)

q Creating a Grid Theme from the Image analysis theme for analysis using Spatial Analysis Extension:

(a grid theme allows for the display and editing of the attribute information associated with the image file)

1. Make theme active and zoom in to a small area of interest e.g. county, township, section etc (to reduce processing time and disk space) or simply overlay boundary data of your choice.

2. Go to Image Analysis Menu and click on Properties and set the Analysis Extent to “Same as Display” (if you want to clip the current extent in the view window) or select a boundary theme to use for clipping the image file) and click OK.

3. Click on Subset in Image Analysis menu.

4. Select Grid in List of Files Types to convert image to a Grid format.

5. It may take some time check the status bar.

· OR

6. Go to the Theme Menu and select Save Image As and select Grid in List of Files Types to convert image to a Grid format. Name and save the output file.

7. When asked to add new theme to the view click “YES”.

11. Notice that the output Grid theme comes with the original legend.

Note: sometimes it may be necessary to close the current project window and open a new one or exit and restart ArcView in order to have the grid theme displayed with associated attributes.

q Using Spatial Analysis Extension to support spatial analysis.

1. Open a new view from the project window, rename the view “Spatial Analyst”

2. Go to File Menu and select Extensions.

3. Under Available extensions scroll down and check the box next to Spatial Analyst.

4. Click OK to load the extension into the GUI, when loaded the Menu interface changes and has Analysis and Surface Menu added. Also notice a Histogram Button and a Contour Tool added to the tools menu.

5. In the view Add Theme and select Grid Data Source as a data source type

6. You will notice that no Grid files exit in the CD-Rom.

7. Navigate to the directory/folder you saved the Grid File in step 11 above and select the file and add to the view.

8. Does the TOC contain a legend for the image? Notice also that the Open Theme Table button is active.

9. Display the theme into the view. Open the Legend Editor and check the options available in the Value Field.

10. Compare the identify results between the different themes. Which theme gives more attribute information?

q Querying grids: create a map query

1. Open the Grid theme table and with the select tool click on a record to highlight it. All grid cells with the selected value are highlighted in the view as well.

2. If you want to create a new image containing the highlighted categories go to Theme menu and select Convert to grid in order to create an image of just the selected/highlighted land use.

3. Resymbolize the grid theme by changing fields in the values field of the legend editor. Also remove the no data with the null values button.

4. Find areas of particular land use, from Analysis menu, choose Map Query and create an expression (by double clicking a layer of your choice, click an operation sign =, and double click unique value of choice)

e.g. ([grid name]=”sunflowers”)

5. Click Evaluate

6. You can edit the expression to modify the query

e.g. ([grid name]=”sunflowers”) and (acres>=amount)

q Creating image subset: i.e. breaking out a portion of a large file into one or more smaller files to reduce file size and speed-up processing time.

ND State land use Regional subset Ramsey County subset

Creating image subset for analysis

1. Make the Image Analysis land use theme active in the legend

2. Define the Area of Interest (AOI) by zooming in or drawing a polygon (rectangle, cycle etc.) or by adding/overlaying a feature theme e.g. county boundary theme to define AOI. You can also digitize a custom polygon themes (watershed, aquifer, soil class) using View Menu to create a polygon New Theme and use drawing tools

3. Open Image Analysis properties menu and input the following:

· Analysis extent = Same As Display to clip image according to size in the view OR input the name of the feature theme defining AOI

· Analysis mask = input the feature theme defining the exact boundary to clip, that is the AOI theme.

· Click OK to close the window.

4. Open Image Analysis menu once again and select on Subset in (you can also achieve the same by using Save Image As in Theme menu).

5. Try to query the attributes of the new image.

q Creating a new image for a selected number of land use from the existing image.

Multi-land use map Single-land use map

1. Make Grid Theme active.

2. Open Theme Table and select land use of interest.

3. Notice that the selected land use is highlighted in the display.

4. Go to Theme and select Save Image As and click OK

q Reclassifying a land use image into broad categories e.g. cropland, pastureland, water bodies and other. Usually done to combine several classes into broader categories.

Original land use map Reclassified land use map

(4 broad categories)

1. Create a GRID theme and make it active in the view.

2. Make sure the theme is added as a GRID data source.

3. Open ANALYSIS menu and select RECLASSIFY from the menu.

4. In the Classification Field dropdown list choose VALUES field as a field to be reclassified.

5. Change land use VALUES in the New Value column by assigning a common value to all known crop values. Assign unique common values to pastureland, water bodies and other.

6. Click OK and when the process is done display the new reclassified image.

· NOTE: the new values column can be single values or No Data.

q Generalizing a land use image: in order to clean or remove isolated pixels that do not belong to the major category.