layer of rivers is added to the map and placed at the top of the Contents pane. The layer is symbolized with a random color; if the color is difficult to identify, it may be beneficial to change its color using the color palette. (If you are having trouble, refer to the task “Set layer properties,” steps 1 and 2 earlier in this section, for instructions.)
2)Click on any river to identify it.
You see the name of the river (many of them don’t have names) and its other attributes.
By default, the Explore tool identifies features from the topmost layer in the Contents pane. If you miss a river, you’ll identify either the city of Los Angeles or nothing. That’s fine—leave the Explore window open, and click again on a river.
3)Click on a few more rivers to identify them. Try to identify a segment of the Los Angeles River.
The river runs west to east across the city, turns south near the city’s eastern edge, and follows a freeway to San Pedro Bay.
4)Close the pop-up window.
Make a definition query on the Los Angeles River
Just as you’re mainly interested in one city, you’re also mainly interested in one river. You’ll make another definition query to show just the Los Angeles River.
1)In the Contents pane, right-click the River layer and click Properties.
2)In the Layer Properties: River dialog box, click Definition Query.
3)Build your query:
Name is equal to Los Angeles River.
4)Click the General tab. Change the layer name from River to Los Angeles River.
5)Click OK.
The Contents pane reflects the new layer name.
Change the symbology
1)Click the color symbol below the Los Angeles River name to modify the symbol. Clicking the symbol opens the Symbology pane on the right side of the map.
2)Click the Properties tab at the top. Under Appearance, you can change the color and width of the symbol.
3)Change the color to blue.
4)Change the line width to 3 pt.
5)Click the Apply button, and close the Symbology pane.
On the map, the river is displayed with its new symbology.
Select Los Angeles River features using a query
On the map, the river looks like a single feature (just like the city), but it’s not.
1)In the Contents pane, right-click the Los Angeles River layer and click Attribute Table.
At the bottom of the table, you see that 0 of 17 records are selected. That means that, in this particular layer, the Los Angeles River is composed of 17 features. Why is that?
2)Scroll down through the table.
All the records have the same name value. Most have the same type, but one is an artificial path. There are a few description values. The need to maintain different attribute values for different parts of a geographic object is a common reason that data—especially data representing linear features such as streets and rivers—is constructed this way, consisting of multiple features. We’ll come back to this point in lesson 2.
3)In the ribbon of tools on the Map tab, in the Selection group, click the Select By Attributes button
Having noticed “perennial” (year-round water flow) and “intermittent” (not year-round water flow) values in the description field, you might want to know which parts of the river are which. You can find out using an attribute query. An attribute query is like a definition query in that both types of query single out features in a layer on the basis of attribute values. The difference is that an attribute query highlights (selects) features that satisfy the expression rather than hiding features that don’t.
4)In the Layer Name or Table View box, confirm that Los Angeles River is selected.
5)Make sure the Selection type drop-down list is set to New selection.
6)Click the Add Clause button.
7)Create a clause for
Description is equal to perennial.
8)Click Add.
9)Click Run, in the lower-right corner of the pane.
Twelve records are selected in the table. The corresponding features are selected in the map, showing that the river is perennial for most of its length.
It’s not among your guidelines to locate the new park along the river’s perennial stretch, but it’s interesting that fairly simple data exploration may introduce new ways of thinking about your problem.
10)Close the Select Layer By Attribute Geoprocessing pane.
Find the length of the perennial portion of the Los Angeles River
As you learned by looking at the attribute table, the perennial portion of the Los Angeles River is separated into 12 distinct records. To find the total length of this section, you must perform a summation of the FEET fields, using the Summary Statistics tool. When features are selected in the layer, the Summary Statistics tool processes only the selected records as a subset. Because you have perennial streams selected, the tool will sum up only the SUM field of these selected features.
1)In the attribute table of the Los Angeles River layer, right-click the DESCRIPTION field and click Summarize.
2)Rename the output table LARiverPerennial by clicking the Browse
