USING ARCVIEW

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Step 14: Advanced Features in ArcView

Drawing Themes in ArcView

Such themes are very useful for adding new information to a map about an area or to create features to display values at particular places.

Let us add a few points to a map and then add attribute data to the new point theme's table.

Let us start a new project. If you have a project already open, you need to close it. To do so, start a new project by selecting from the menu at the top File and then Close from the drop-down list. Then click on File again and select New Project from the drop-down list. You can save your edits before you exit your current project, if you want.

If you are just starting the ArcView program, open a new project as we did in an earlier lesson.

In the new project, add the theme "bpkprcl.shp" and make it appear on the map.

Then select from the menu at the top View and New Theme from the drop-down list.

The New Theme window appears, asking you to select which "Feature Type" you want to create--point, line, or polygon--from a drop-down list.

Select Point and click on the OK button. The New Theme dialog box appears, requesting the file name for your new theme and which directory to use to store the theme. I selected the file name "point.shp" and placed it in the CARDI directory.

Click on the OK button and notice that the small box next to the theme name "Point.shp" in the Table of Contents has a thin dashed line around it. The dashed line means that you are in edit mode for that theme.

Note that even though the box next to the theme name has a check in it, no data appear on the map because the theme now is empty. ArcView wants us to create the points and associated attribute data that will be stored in the theme.

Click on the Draw Point button in the second row of buttons at the top of the screen. Your cursor changes to a cross-hairs. Clicking once on the screen will place a point there with handles around it.

Click on three other places to establish points there.

Click on the pointer arrow in the second row of buttons on the far left at the top of the screen. Then click once on the map to remove the handles.

Now click on the Open Theme Table button in the top row of buttons at the top of the screen. Notice that there is only one field--"Shape"--in the table Attributes of Point.shp.

If you click on Table in the menu at the top of the screen, you see the choice, "Stop Editing" in the drop-down list, which means that we are already in Edit mode.

Thus, unlike before, we do not have to select "Start Editing" to make changes or additions to the table.

Go ahead and add a field (select Edit and then Add Field from the drop-down list) and call it "Insects." Be sure that in the Field Definition dialog box that the "Type" is "Number." Click on the Edit button in the second row of buttons at the top of the screen.

Then you can add numbers to the table.

We can add any number of fields to the new table, but we will only create one new field here. (We could also add data in the form of "categories" if, when adding the new field, we had selected for the "Type" the choice "String.")

Select Table from the menu at the top and Stop Editing from the drop-down list. Respond Yes when queried if you want to "Save Edits?".

Close the table and double-click on the theme name "Point.shp" in the Table of Contents to bring up the "Legend Editor" dialog box.

Select "Graduated Symbol" for "Legend Type" and "Insects" for the "Classification Field" and then click on the "Apply" button and close the "Legend Editor" dialog box.

The values for our new field are now illustrated by the graduated symbols on our map.

Thus, we can map the new points that we created and assign values to them. For example, the points could represent pest traps in a garden. A major advantage of creating such themes is that you could create a theme that had several data points (such as different pest traps) in the same garden or tract.

In addition, you can draw lines and polygons to create new themes in the same manner.

Spatial Joins

We need to combine the tables of the two themes to perform the spatial join.

Let us say that one theme has point data on pest counts and the polygon theme represents landuse. The spatial join will allow us to summarize the pest count data by landuse.

Add the themes "Bpkcrops.shp" and "badpests.shp" so that they appear on our map in the view and click on the boxes for "Point.shp" and "bpkprcl.shp" in the Table of Contents to remove them from our map. Display the data for the field "Landuse" in the theme "Bpkcrops.shp".

To perform the spatial join, first open the table for the polygon theme "Bpkcrops.shp" and click on the field name Shape.

Now open the table for the point theme "Badpests.shp" and also click on the first field name Shape as well.

(Note: You should open the polygon theme first and the point theme second to perform the spatial join, as we did here.)

Click on the Join button . The data from our two tables are now merged in the table "Attributes of Badpests.shp."

Scroll to the right to find the column heading "Landuse". Note that for each record in our table that the type of landuse is now specified. Click on the field name "Landuse" so that its cell appears darker.

By selecting this field, we can summarize the pest count data according to the type of landuse.

We can now summarize the data to determine the total pest counts by land use. Click on the Summarize button in the top row of buttons.

In the Summary Table Definition dialog box, under "Field" select "badpests" from the drop-down list. Under "Summarize by" select "Sum."

Click on the Add button and the category "Sum_badpests" will appear in the empty box on the right.

Click on the OK button. The results now appear in a new table.

Now we know the total number of "badpests" in each type of landuse.

Thus, we can combine data in two different themes to examine their relations.

Hot Links

We are going to add a hot link to the largest point in the theme "Point.shp." To do so, first select the largest point so that it appears yellow on our map.

Then open up the attributes table for "Point.shp". Add a new field. In the Field Definition dialog box, Name the new field "Image" and be sure that its Width specified in the Field Definition dialog box is wide enough to contain the entire address of the external image that will be linked to the point (I set the width at 40 in this case). Also, be sure to set the Type as a String because we are typing in a category, not a number.

The table should look like this:

In the row that is highlighted in yellow (which represents the largest point on our map), go to the field "Image". Type in the "address" for the image that will be the hot link to our selected point. We want as our hot link the image file "bug.gif", which is located in the cardi directory. Thus, its address is:
C:\cardi\bug.gif
Type in this address.

Go back to our map and open up the Theme Properties dialog box. On the left hand side of the dialog box, scroll down to the Hot Link icon and click on it.

In the drop-down list for Field, select "Image", which has our address of the image.

For the drop-down list for Predefined Action, select "Link to Image File."

Click on the OK button.

Go to the Hot Link button in the second row of buttons at the top of the screen and click on it. When you move your cursor over the map, it appears like a bolt of lightening. Click once on the point highlighted in yellow to bring up the hot-linked image of the insect pest at that garden.

We could also have as our hot links pictures of garden crops infested by insects or of charts displaying some information of importance. Similarly, we could have two themes loaded of the same shapefile representing the same garden at two different points in time and have a hot link for each one to see what the condition of the garden was like at the two different points in time.

The End... and the Beginning

Also, we have only examined the basic ArcView software package. There are more advanced modules available to allow you to perform much more complex analyses.

I hope this workshop has stimulated your interest in using GIS to enhance your work.

Good luck!

Larry Grossman August 14, 1998

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