AA, AB, AC on November 5
AD, AE, AF on November 6
Completed answers to the questions in Parts A and B and process diagrams. (Find the answer sheet
and blank diagrams in p:/Geog460au03/Data)
At version 8.1, ArcMap's query tool is built into the Raster Calculator tool. Cells that satisfy the condition entered in the calculator dialog box will be assigned the value "1" and those that do not will be assigned "0". This tool is VERY picky about the use of syntax in formulating these operating statements. The most frequent mistake is in the use of parenthesis, "(" and ")", to group operations. The exact code for each transformation is being supplied to help reduce frustration caused by mistakes in creating the operating statement. In the long run you will need to learn how to type these text strings accurately to be able to perform your projects.
Raster Calculator is also picky about the location of the
grid datasets it uses. It prefers that the grid datasets are located
in the working directory. This is why you were asked to move your
grid datasets from the Data folder into your student folder, and
then set your student folder to
be the working directory.
To get a better idea of layers and how to use them, you'll
want to read the following sections of the ArcMap Help. Click
on the 'Index' tab in the help window and enter 'Layers' in the
keyword window. You'll see a list of additional information topics
available for 'Layers'. You'll see a
list of additional information topics available for 'Layers'.
To better understand layers read these sections: under 'layers'
double click on 'described' in the pop-up window double click
on "Layers, data frames and table of contents" (of special
interest here is the section on "How layers
reference data") under 'layers' double click on 'referencing
data sources' you'll want to read both sections that appear as
options in the pop-up window.
Layers provide an ability for ArcMap to connect a data source with symbology. This arrangement is useful to preserve relationships between maps and source data in situations where the data is being edited or updated. ArcView 3.x used 'legend' files (.avl) to store symbology and map representation for various data sources. ArcMap no longer uses this arrangement and has replaced it with the Layer. In class we are working to provide you with access to data and symbology to help you develop your understanding of the core concepts. Layers contain symbology and a pointer to the data set to be displayed. If you copy a layer from one location (p:/Geog460aut03/Data) to your working directory it will still 'point' to the original location of the data used to create the Layer. Moving/copying a layer is often a two step process: Move/copy the layer, move/copy the data then re-point the layer to the new data location using the 'Set Data Source' button. This information is useful to understand the steps in this and other exercises as well as managing your data/maps for your project. Please explore the other help options available for 'layers' so you can effectively use their capability and not be frustrated by their weaknesses.
As part of this exercise you will begin filling out process diagrams. These show the layers you are working with, the operations you perform on them, and the new layers that are made by the operations. Obtain the process diagrams on the P drive, see instructions. This will be turned in with your answer sheet. In future exercises, and in the group project, you will be expected to make your own process diagrams to plan and illustrate your work.
In this part of the exercise you will use Raster Calculator to explore attribute operations (Chapter 4) and map overlays (Chapter 5).
1. Select the Cover1991.lyr. Display it and nothing else.
2. Right-click on Properties> Source. Note that under Data
Source your layer's source is
Folder: P:\geog460aut03\Data\Cover1991 (which is a grid). You
have to change this and make your layer point to the grid "cover1991"
in your student folder (working directory). Click on "Set
Data Source" and select the grid file "cover1991"
in your student folder. Now the source for "cover1991.lyr"
in your student folder is the "cover1991" grid in your
student folder. Wait for the change to appear in your window,
and then click "Ok".The reason you do this is
to avoid problems with the picky Raster Calculator.
3. Open the layer attribute table and the Layer Symbology window
(Right-click on layer title -> Properties -> Symbology),
and look at what values are used for Coniferous Forest and Deciduous
Forest. Close the table and Layer Property dialog.
4. Select: Spatial Analysis > Raster Calculator.
5. Use the pointer and keypad to select layers and operators to
construct the following argument in the Raster Calculator dialogue
window:
[cover1991] == 5 | [cover1991] == 6
(This means you want the cells that have "value equals 5
or value equals 6".)
6. Click the Evaluate button.
7. Close the Raster Calculator window.
8. Select the newly created layer, "Calculation".
Right click on layer title, click on Make Permanent to
save it to your working folder on P:\.
9. Open layer property dialog window (right-click -> Properties
-> General) and change the layer name to "Forest 1991".
Question A1:What kind of attribute operation did you do when you made this query? Did it increase or decrease information content?
10. Add "cover1998.lyr" from your student folder. Just as you did for "cover1991.lyr", you have to point "cover1998.lyr" to the "cover1998" grid in your student folder. See step 2 above.
11. Open the layer table attribute table and the Layer Symbology
window and look at what values are used for Coniferous Forest
and Deciduous Forest. After viewing the Forest values, close the
attribute table and Legend Editor.
12. Select: Spatial Analyst -> Raster Calculator.
13. Construct an argument in the command box to select Coniferous
and Deciduous Forest types.
14. Click the Evaluate button.
15. Close the Raster Calculator window.
16. Select the newly created layer, "Calculation".
Display it and nothing else. Right click on layer title, click
on Make Permanent to save it to your working folder on
P:\.
17. Rename the layer as "Forest 1998".
Question A2: Describe how "or" (the logical operator | ) works in the case, and how this relates to the attribute operations described in Chapter 4.
18. Select: Spatial Analyst > Raster Calculator.
19. Construct the following argument in the command box:
Forestchange = ( [Forest 1998] - [Forest 1991] )
In this step, you are providing Raster Calculator with a name for the output grid: "Forestchange". So, the output will be a grid called "Forestchange" as opposed to a grid with the generic name of "Calculation", which you will then have to make permanent and rename. If you right-click on "Forestchange" and go to Properties>Source and look under Data Source, you will see that the "Status" for this grid is "Permanent". So, you do not need to make it permanent as you did for "Forest1991" or "Forest1998". This is a shorter way to create an output using Raster Calculator.
20. Click the Evaluate button.
Question A3: What attribute combination results from
the overlay that you performed? (Chapter
5, Overlay see Lecture 10)
Question A4: What do the values (-1), (0), and (1) represent?
Consider the results of the first two map queries.
In this part of the exercise you will use Raster Combine tool to perform overlay combinations.
1.Select: Spatial Analyst -> Raster Calculator.
2. Enter the function
Coverchange = combine ( [cover1991] , [cover1998])
(You can read more about the Combine function in the Arcmap Help menu. In the Index, type keywords "Raster Calculator, using". Then follow the "Functional Reference" link in the display window. In the "Functional Reference" window, click on the "Search" tab, and type in keyword "Combine". Choose the first hit, titled "Combine" and read about this function. The illustration is particularly useful.)
3. Click Evaluate.
4. Click on "Symbology", choose "Unique
Values", and set the "Values Field" to "Value"
if it isn't already chosen.
5. Open the table for this layer, and read the fields and values.
Question B1: What attribute combination results from
this overlay?
Question B2: What does a Value of "7" mean? (hint:
compare columns in the table) How many cells share this value?
Use specific land cover descriptions in your answer.
6. Select: Spatial Analyst > Raster Calculator.
9. Construct the following argument in the command box:
Fctypes = ([Coverchange] * [Forestchange])
8. Click Evaluate.
9. Close the Raster Calculator window.
10. Open the table for this layer, and right-click the heading
"Value", choose Sort Ascending to sort the values.
(use multiple layer tables to help you answer B3 and B4)
Question B3: Forests were most frequently converted to
which three land cover types?
Question B4: Which three land covers were most frequently
converted to forests?
Version of 24 October 2003