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How do I choose and map a dominant component in ArcView 3.2?

Once you have your data ready to use in ArcView, you'll need to open up the comp table. The first step is to sort the data. To do so, select the comppct field by clicking on its header and then click the Sort Descending button Sort Button.

Next we will summarize the data. Note that in this example, I am using data that is in the same table, comp, as the comppct field that I am using to sort. If I needed data from another component-level table, I would join the two tables. An explanation of joining tables can be found near the bottom of this page. To summarize the data, first select the Musym field. This field identifies the mapunits. Since the table contains component-level data, there are many cases where there are two or more data records (each indicating a component) for the same mapunit. Summarizing allows us to calculate one value for each mapunit, thus combining the values of the different components. With the Musym field selected, click on the Summarize button Summarize Button . This will bring up the following window:

Summarize Window

In this window we set the filename for the new table and we designate the fields we want to create in the new table. In this example, we are going to summarize the Drainage field - meaning that we will be taking the Drainage values for the various components in each mapunit and reducing them to one value. Since the Drainage values are qualitative our only choices are First and Last. We have already sorted the table so that the components with a higher percentage of the area are listed first, so we take the first Drainage value. This is the Drainage value for the dominant (or largest) component. When we click 'OK' in the window, a new table is formed.

Sum Table

The new table has three fields: Musym, Count, and First_Drainage. Musym is the mapunit identifier - remember that Musym was the basis for our summarization. Count is the number of records that had each mapunit symbol. This field will be filled with many 1's, 2's and some 3's. First_Drainage is the new field that we created. However, we still cannot map First_Drainage. First, we must join the table to the table for a View.

In our new table, highlight the Musym field. Now, open a View containing one of the soil maps. Then click on the Open Theme Table button Open Table Button . In this table select the Musym field. With the theme table active, click on the Join button Join Button . This adds the other two fields from our summarization table to the theme table. Now we can use the First_Drainage field for mapping. You can see the results below:

Drainage Map