The GIS 20. Gina ClemmerЧитать онлайн книгу.
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TIP To “deactivate” any of the other tools, click the default pointer. This button removes the first tool and activates the default pointer.
The Identify tool
Identify is one of the most useful tools. You can use the Identify tool to click specific geographies and look at the underlying data. Use the Zoom In tool
1 7.Click the Identify tool, and then click a county. Notice that a box with county information appears. Try a few more counties until you are comfortable with this tool. Click the default pointer to get rid of the Identify tool.
Explore the table of contents
The Table of Contents window, located on the left side of the ArcMap window, is the organizational panel for working with files in ArcMap. Notice two shapefiles listed in the table of contents under Layers in the illustration. Also notice the five buttons at the top of the table of contents: List By Drawing Order, List By Source, List By Visibility, List By Selection, and Options. Hover over any of these buttons in ArcMap, and a description of what that button does displays.
1 1.Click the first button, List By Drawing Order . The default is the second button, List By Source ; however, List By Drawing Order is more useful for most edit sessions.
2 2.Use the Zoom In tool to zoom in to your state.
3 3.Display layers by selecting the box next to each layer to turn it on, or by clearing it to turn it off.
4 4.Practice moving the county shapefile and the places shapefile. Move layers up or down by highlighting the layer in the table of contents (clicking the layer once) and dragging it to the desired position. Notice how your map changes as you reposition the layers. When the place layer is on top, you can see cities in your state. When the county layer is on top, it blocks out the place layer because it is the top layer and has a solid fill color associated with it. Move the place layer into first (top) position.The layer names are what will be used in the legend. You may want to make them more reader-friendly by renaming them to common names such as Counties and Cities.
TIP This functionality will work only while in List By Drawing order mode. If you are unable to move these layers up or down, click the first button, List By Drawing Order, and try again.
1 5.Click the layer name twice to activate the text. Type over the existing layer name. The layer is not renamed in the underlying data, but only in your map.
View data
Shapefiles contain two things: the map and the underlying data table. So far, you have looked at the map part of the shapefile and used the Identify tool to look at the underlying data. Another way to view the underlying data is to view the whole data table at once.
1 1.In the table of contents, right-click the county layer name, and then click Open Attribute Table. Use the scroll bars (right, bottom) of the attribute table to better understand what is available in the underlying data table. You should notice a few thousand counties in the attribute table. There is no demographic data here, only FIPS codes, county names, and some other miscellaneous codes and information the Census Bureau included when it created the shapefile.
2 2.Right-click any of the column headings, and then click Sort Ascending. Notice that this command sorts the entries alphabetically (if the entry contains text) or from smallest to largest value (if the entry contains numbers). This command is useful when you need to isolate a few entries in a large group.
1 3.Close the attribute table by clicking x in the upper-right corner.
Customize shapefiles
Shapefiles downloaded from the Census Bureau, or anywhere else, may need to be modified to suit your purposes. A great example is when you downloaded the county file. You had no option to download a county file only for your state. The only file given was at the national level, containing all counties for the entire US.
For the following exercises, it would be better to have a shapefile of counties only in your state (like the place shapefile). How do you do that? The Census Bureau does not provide the shapefiles that way. However, it is easy to carve up shapefiles. In the next few steps, you’ll isolate your state’s counties and create a new shapefile that contains just those counties.
1 1.In the table of contents, right-click the place (Cities) shapefile, and then click Open Attribute Table.
2 2.Find the column titled StateFP (the third column from the left), and make a note of your state’s two-digit FIPS code. For Alabama, this code is 01. Close the attribute table.
1 3.In the table of contents, right-click the county file, and then click Open Attribute Table.
2 4.Right-click the StateFP column heading, and then click Sort Ascending to organize the table by state. Scroll down and find the first record in the StateFP column that corresponds to your state’s FIPS code. Finding the code for Alabama is easy. The code for the state is 01, so the counties in this state are at the top of the attribute table.
1 5.Once you find the first record for your state, click the first gray cell at the beginning of the row that contains the first record for your state. Clicking the cell creates a bright-blue highlighted record on that line item. Continue to highlight the remaining records for your state by dragging the mouse down the records (you must be on the beginning gray cells to drag highlighting). Highlight all records in your state.
2 6.It is important to close the attribute table now. Notice that counties in your state are highlighted on the map. The attribute table and map are linked. You may need to zoom in to see your state more closely.
Now you’re going to create a new shapefile for just those counties in your state.
1 7.Right-click the Counties layer name in the table of contents. Click Data, and then click Export Data. Leave all default options, except click the Browse button and navigate to your save folder (under Folder Connections).
1 8.Name the file your state’s name plus Counties—for example, “AlabamaCounties.” From the “Save as type” list, select Shapefile. Click Save, and then click OK. When prompted with the box that says, “Do you want to add the exported data to the map as a layer?” click Yes. Notice that a new layer appears in the table of contents.
Now you can organize things a