Understanding GIS. David SmithЧитать онлайн книгу.
that symbology. In this book, for instance, you’ll draw the outline of Los Angeles in other map documents in coming lessons.
You can save layer properties to a file called a layer file, which has the file extension .lyrx. A layer file is not a copy of the data, but you add it to a map document in the same way that you add data. The layer file stores all the properties of a layer—its name, symbology, definition query, and so on—including the path to the layer’s source dataset. When you add a layer file to ArcGIS Pro, the layer draws with its properties already set.
1)In the Contents pane, right-click Los Angeles and hover over Sharing. Select Save As Layer File.
The Save Layer(s) As LYRX File dialog box opens.
2)Click Folders at the top of the left column and open the ParkSite\MapsAndMore folder.
3)Name the new file LosAngeles (no spaces) and click Save.
Now you’ll remove the Los Angeles layer that’s currently in the map, and then add the layer file to see how it works.
4)In the Contents pane, right-click Los Angeles and click Remove.
The layer disappears from the map and the Contents pane.
5)In the Catalog pane, browse to the MapsAndMore folder.
6)Drag the LosAngeles.lyrx file above the Los Angeles River layer in the Contents pane.
The layer is added to the map with all its properties set (layer name, symbology, definition expression, and so on).
7)Open the layer properties of Los Angeles. In the Layer Properties dialog box, click Source.
Note that as before, the layer points to the City_ ply feature class. As stated previously, layer files do not store raw data; they are a pointer to the GIS data along with the properties about how to display the data on a map.
8)Close the Layer Properties dialog box.
Anytime you add the LosAngeles.lyrx file to a map document, the layer will draw as a yellow outline with a definition query on the city of Los Angeles. Once the layer is added to the map, however, it’s just the same as any other layer, and you can change its properties however you want. (Not that you want to change them.)
Follow the river
Now you can start developing a sense of the study area by following the river’s course through the city.
1)Maximize the ArcGIS Pro window if you haven’t done so already.
2)Open the City of Los Angeles bookmark.
3)Zoom in on the river’s source in the community of Canoga Park in northwest Los Angeles.
The river officially starts where Bell Creek and the Arroyo Calabasas converge at Canoga Park High School.
4)Click the Map Scale drop-down arrow below the map and click 1:24,000.
5)Press and hold the left mouse button to pan slowly eastward along the river.
Densely populated residential neighborhoods line both sides of the river until you get to the Sepulveda Dam Recreation Area, a large recreational area with golf courses and a lake. The river bottom is natural here, becoming concrete again at the Sepulveda Dam in the southeastern corner of the basin.
Setting map scale
By default, map scale is displayed in the form of a representative fraction, such as 1:24,000. At this scale, for any unit of measure, one unit of distance on the map is equivalent to 24,000 units in the real world. You can set the map to any scale you want by typing a number in the scale box and pressing Enter. You can also enter a verbal expression such as “1 inch = 1 mile,” and it will be converted to a representative fraction. To change the way that scale is displayed, or to change the list of predefined scales, click Customize at the bottom of the Map Scale drop-down list.
East of the Sepulveda Basin, the river follows a freeway for a while and is again surrounded by fairly dense residential and commercial areas.
6)On the keyboard, press and hold the Q key.
Now you roam continuously across the display in whichever direction you point the mouse. To control your speed, make small brushing movements with the mouse either with or against the direction of movement. As you roam, the imagery should draw smoothly and continuously, although your experience may vary. Other layers, such as the Los Angeles River layer, suspend drawing and catch up when you stop.
7)Release the Q key to stop roaming.
8)Continue to pan (or roam) along the river.
The river flows generally southeast for a while and then follows the northern edge of unincorporated Universal Studios. It continues east and then bends sharply south as it curves around Griffith Park (at 4,218 acres, one of the largest city parks in the United States). To the north of Griffith Park lies the city of Burbank; to the east is Glendale.
As it flows south, the river runs parallel to another major freeway. You’ll see the Silver Lake Reservoir and then Elysian Park, where the Los Angeles Dodgers play Major League Baseball.
Create Dodger Stadium bookmark
Dodger Stadium is a landmark that you may want to return to, so you can save the map location (or “extent”) as a bookmark.
1)Center your view on Dodger Stadium, more or less as shown in the figure.
2)On the Map tab, click Bookmarks > New Bookmark.
3)In the Create Bookmark dialog box, name the bookmark Dodger Stadium and click OK.
Pan to the city limits
You’ll follow the river until it crosses the LA city limits, which marks the boundary of your study area.
1)Pan along the river as it runs south.
This last section of river passes through an industrial landscape and leaves the city at the Redondo Junction train yards.
2)Close the Lesson1a map view (not the entire project) and any open tables.
3)Save your project.
4)Continue to exercise 1b or close ArcGIS Pro. Save your changes if prompted.
Results for the book’s exercises can be found online on the book’s resource web page. For information on how to download and use the Results data, go to esri.com/UnderstandingGIS4.
Exercise 1b: Do exploratory data analysis
In this exercise, you’ll add park data and census data (containing demographic and socioeconomic information) to your map. The goal is to pay attention to patterns in the data and thereby build an intuitive sense of likely and unlikely locations for the park. This intuition should give you confidence that the analysis results you get in lesson 6 are plausible. Conversely, if the results contradict your gut feeling, you may be alerted to possible mistakes in the analysis.