Understanding GIS. David SmithЧитать онлайн книгу.
Contents pane, right-click the color patch underneath the City_ply layer name. A color palette opens. Pointing to any color square shows its name as a ToolTip.
2)On the color palette, click Olivenite Green.
On the map, the cities redraw in the new color.
3)In the Contents pane, right-click the City_ply layer name to open its context menu. At the bottom of the menu, click Properties.
The Layer Properties dialog box opens. Here is where you access the full set of properties for a layer.
4)If necessary, click the General tab at the top of the left column on the dialog box.
The layer’s name, City_ ply, is one of its properties. This name is cryptic (it stands for “city polygons”) and unattractive, so now you can change it.
5)In the Name box, delete the text and type Cities.
6)In the Layer Properties dialog box, click the Source tab.
This tab shows technical information about the layer, including the path to the data on your computer.
7)Click OK on the Layer Properties dialog box to close it.
Notice that the name is updated in the Contents pane.
Renaming the layer in the map simply makes it easier to identify in the map. It doesn’t change the source data file’s name (which is still City_ ply). A layer is a representation or rendering of the data, not the data itself. You can make any changes you want to a layer’s properties without affecting the data on which the layer is based.
Get information about cities
Now see what you can find out about the cities on the map.
1)Click any city polygon on the map.
The city flashes blue, and a pop-up window opens. In the title bar of the pop-up window, you see the name of the city you identified. In the pop-up window, you see its attributes, or the information that this layer stores about cities. Some of the attributes aren’t obviously meaningful, but others are. If POP2010 is population for the year 2010, and POP10_SQMI is population per square mile for the same year, you know that Los Angeles (if that’s the city you identified) had 3,792,621 inhabitants at the time of the 2010 census, and its population density was 8,018 people per square mile.
2)If necessary, move the pop-up window away from the map. Identify a few more cities.
The pop-up window updates with information about the new city. All the cities have the same set of attributes; it’s the values of the attributes that change.
3)Close the pop-up window.
4)In the Contents pane, right-click Cities and click Attribute Table.
5)Scroll across the table, if necessary, to look at all the field names (the gray column headings).
This is a different presentation of the same information you saw when you identified cities on the map.
6)Scroll back to the beginning of the table, and then scroll a little way down through the records (the table rows).
This table has a lot of records: in fact, 29,259 of them, as you can see at the bottom. Each record corresponds to a unique feature—that is, a unique city—on the map. So there must be a lot of cities you’re not seeing in the current view.
7)Leave the table open. It will stay docked under the Lesson1a map.
8)In the Contents pane, right-click the Cities layer. On the context menu, click Zoom To Layer.
The map zooms out to the geographic extent of the layer: the entire United States. You can’t distinguish individual city polygons at this scale.
9)On the Map tab, in the Navigate group, click the Previous Extent button.
Select the record for Los Angeles
When you select a record in an attribute table, the corresponding feature is selected on the map. (Likewise, when you select a feature on the map, its record is selected in the table.) Selections are marked with a blue highlight by default.
1)Scroll up to the top of the table. Make sure the table is wide enough that you can see the POP2010 field.
2)Right-click the POP2010 field name. On the context menu, click Sort Descending. Alternatively, double-click the column header to switch between the ascending/descending sort order.
The records are sorted in the order of their populations, from largest to smallest. Los Angeles is now the second record in the table, after New York.
3)At the left edge of the table, click the small gray box next to the Los Angeles record to select it.
On the map, the city of Los Angeles is outlined in blue. You may be able to see the whole city already, but now you can make sure.
4)Close the attribute table by clicking the X to the right of Cities.
5)In the Contents pane, right-click Cities and click Selection > Zoom To Selection.
The map zooms in close on the selected feature and centers it in the view. The city’s odd shape is attributable to years of piecemeal expansion and incorporation. The city has internal “holes” where it surrounds other cities, such as Beverly Hills, or unincorporated areas. It also has a long, narrow southern corridor that connects it to its harbor at the Port of Los Angeles.
6)On the Map tab, in the Selection group, click the Clear button
Filter the display of cities using a definition query
One of your project requirements is that the new park be inside the Los Angeles city limits. Therefore, you’re more interested in Los Angeles than in other cities. A layer property called a definition query allows you to show only those features in a layer that interest you.
1)In the Contents pane, right-click the Cities layer and click Properties.
2)In the Layer Properties dialog box, click Definition Query.
3)Click Add Clause to begin building your query.
You build a query on an attribute table by specifying a field and setting a logical or arithmetic condition that values in that field must satisfy. In this case, you want to find records with the value of Los Angeles in the NAME field.
4)In the list of field names, use the drop-down arrow to click NAME.
5)Click is Equal to in the second drop-down menu.
6)Type