Themes

Most of what Arcview consists of is themes. The theme is the one of the most important components of GIS. A view consists of one or more themes layered on top of each other. In this section, the following parts of a theme will be covered:

Exercise

The concepts covered in this exercise will be:

Adding a Theme

Suppose you wanted to use another theme not present in the View. The theme has to be added.

Deleting a Theme

Legend and Symbol Editor

Legend Editor
The Legend and Symbol editor change the way data looks either through changes in the feature classification or through changes in the legend itself.

Classification of a Theme

Classification of data involves grouping data so that the data is more understandable. There are different ways of classifying data, only a few of which will be explained here:

Exercise

In this exercise,various concepts of classification are covered.
  1. Go to the File menu and select Close All. This closes all open windows in the project. Go to the File menu and select New Project. When the dialog box pops up asking whether to save changes. Click No.
  2. Highlight the View icon and click New. Maximize the ArcView GIS and view1 windows.
  3. Click on the button titled Add Theme. When the dialog box opens up, double click on the c:\ folder and then double click on the basins folder. This folder contains all the data for the Cahaba River.
  4. Double click on the folder named "data" and then on the folder named 03150202.
  5. On the left there will be a listing of all shapefiles which can be themes. Hold down the Shift key and select dam.shp, rf1.shp, cat.shp and cnty.shp. You will need to scroll down the list to find all the themes. Release the shift key. Click OK. Turn all themes on.
  6. Go to the View Menu and select Properties. Highlight View1 in the Name field and type in any name(for ex: Cahaba) for your View. Click Ok.Notice the name change in the View window.
  7. In the Table of Contents, make sure the order of the themes are as follows:rf1.shp, dam.shp, cat.shp, cnty.shp from top to bottom. This is to ensure visibility of all themes. If this is not so, click and drag the theme(s) so that they are in the proper order.
  8. The dams are hard to see because the circles representing them are too big. Open the symbol editor for the dam.shp theme by double clicking on the theme's name in the table of contents. Notice the symbol in the symbol box is a dot. Double click on the dot in the symbol box. This opens the symbol editor. Click the drop down arrow in the size window, scroll up and click on 4. A 4 should appear in the size box. Exit the symbol window by clicking on the X in the upper right hand corner. Click apply in the legend editor. Exit out of the Legend Editor.
  9. Double click on the cnty.shp theme to open the Legend Editor. Currently the legend type is Single Symbol. Click on the "Legend Type" drop down box and select Graduated Color. The Editor's appearance changes. Click on the drop down box in the "classification field" and select Area.
  10. The classification field is the attribute shown on the theme. Therefore, in this theme different classes of area will be shown on the Alabama county map.
  11. Click on the classify button. Change the type to Quantile by clicking on the "Type" drop down box and selecting Quantile. Click on the Number of classes drop down box and select 3. Click Ok.
  12. Under the Normalize field, you see a row of boxes under the headings: symbol, value and label.Highlight the first box under the heading Label. Highlight the value and type Low. Highlight the next Label box and type Medium and in the next, type High. Click apply. The Quantile classification is customized for your presentation where the distribution of area among the counties is divided into low, medium and high. Close the Legend Editor.
On the right side of the Table of Contents, the county map has been classified using Graduated Color with the county area as the classifying field and classifying method is Quantile.

Summary:In this exercise, you learned to open a new project, change the symbols and colors of a theme and change the legend type and classification method of a theme. You also learned to customize a given classification method.


Unit Summary: :In this unit, you learned how to add a theme, delete a theme, customize a classification, open a new project and also had a brief introduction to the symbol editor.

If you want to go to the next unit, keep Arcview running and do not delete any theme.


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