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Lesson 5 - Posting Data Points and Working with Overlays
Post maps are created by placing points on a map and labeling the points. Posting data points on a map can be useful in determining the distribution of data points, as well as placing data or text information at specific points on the map. Data files contain the XY coordinates used to position the points on the map. Data files can also contain the labels associated with each point.
When a new post map is created, it is independent of any other maps in the current plot window. When the two maps are displayed, notice that two sets of axes are also displayed, one set for each map. When you use the Map | Overlay Maps command, the two maps are combined into a single map overlay with one set of axes. See Chapter 13, Positioning and Overlaying Maps for more specific information on creating map overlays.
To overlay maps:
- Choose File | Open to display the Open dialog box. Choose TUTORIAL.SRF and click the Open button to display the contour map contained in TUTORIAL.SRF.
- Choose Map | Post Map | New Post Map or click the Post Map tool. The^ Open^ dialog box is displayed. This allows you to select the data file used to produce the post map.
- In the list of files, click TUTORWS.DAT and the name appears in the File name edit box. Click Open and the Post Map Properties dialog box is displayed.
- Click the Symbol button and the Symbol Properties dialog box is displayed.
- Choose the filled circle symbol from the Symbol palette and click OK. The selected symbol appears in the Symbol button. This symbol appears at the posted data points on the map.
- In the Fixed Size edit box of the Symbol Size group, specify a size of 0.09 in.
- Click OK and the post map is drawn over the contour map. The contour map and post map are two separate maps on the page. If you look closely at the X-axis, you will notice the two sets of axis tick labels for the two maps.
The Post Map dialog box.
- Choose the Map | Overlay Maps command and the two maps are combined in a single overlay.
The contour and post maps are combined into a single overlay. This places a point symbol at each data location.
Selecting a Map from the Overlay and Assigning an Object ID
After you create map overlays, you can still modify the individual maps in the overlay. Choose one of the three ways to select the maps in the overlay:
- Double-click the maps,
- Right-click on the map and select the Properties command, or
- Select the desired map in the Object Manager and double-click.
The easiest way to select a map in an overlay is to click on the map name in the Object Manager. However, you can also select the map with the mouse. To select an overlapping map in the plot window using the mouse, you often need to use the CTRL key. Whenever two or more objects occupy the same position in the plot window, you have to use the CTRL key to select the desired object. The CTRL key allows you to cycle through the selection of overlapping objects. For example, if you want to select a text block behind a rectangle, or a wireframe map behind a contour map, hold down the CTRL key and click until the object you want is selected. You can use the status bar to help you to select the object.
To select a map from the overlay, and assign an ID to the map:
- Click the map name in the Object Manager (i.e. "Contour"). If the Object Manager is not open, click Edit | Object Manager. The selected map in the overlay is indicated in the status bar. For example, if the selected map were the contour map, the status bar would indicate "Map: Tutorial Contour Map."
- To select the other map in the overlay, click the map name in the Object Manager. Check the status bar, and it should now report "Map: Post."
- When the status bar indicates that the post map is selected, choose Edit | Object ID.
- In the Object ID dialog box, type the name "Tutorial Post Map" and click OK. The status bar reflects the change to the ID for the post map.
The Object ID dialog box specifies the ID for the selected object.
The status bar at the bottom of the Surfer window indicates the selected object in the plot window. In this example, the status bar reports that the post map is selected.
Lesson 6 - Introducing Vector Maps
Vector maps are new to Surfer 7. A vector map is a graphical presentation comprised of a field of small arrows. Each arrow shows a direction and a magnitude associated with the location at which the arrow is drawn. For example, a vector map can depict the local gradients of a topographic surface: the arrows point in the direction of steepest ascent, and the size of the arrows are scaled to the magnitude of the local slopes.
Surfer offers two types of vector maps: a 1-grid vector map and a 2- grid vector map. In a 2-grid vector map the two components of the vectors (i.e. magnitude and direction, or ∆X and ∆Y) are given by two separate grid files. This is described in detail in Chapter 8, Vector Maps.
The two components of a 1-grid vector map are automatically generated from a single grid file by numerically calculating the gradient of the represented surface. By default, the 1-grid vector map draws vectors pointing in the direction of steepest descent, with the vector lengths are scaled by the magnitude of the local slope.
Creating a 1-Grid Vector Map
You can create a 1-grid vector map and overlay it on a wireframe map to produce a map showing the flow of water on a topographic surface.
- Choose the File | New command, or click the New tool. The New dialog box is displayed. Select Plot Document , and click OK. A new empty plot window is displayed.
- Choose the Map | Vector Map | New 1-Grid Vector Map command. The Open Grid dialog box is displayed. The grid file you just created (TUTORWS.GRD) is automatically entered in the File name edit box. Click Open, and the Vector Map Properties dialog box is displayed.
- The default parameters in the Vector Map Properties dialog box create an acceptable vector map. To accept the default parameters, click OK. A vector map is created from
The vector map showing the local gradients of a topographic surface is plotted overlaying a contour map.
TUTORWS.GRD. For more information regarding the Vector Map Properties dialog box, see Chapter 8, Vector Maps.
- Choose the Map | Wireframe command or click the Wireframe Map tool. The Open Grid dialog box is displayed. Choose the grid file TUTORWS.GRD from the list of files, and click OK. The Wireframe Properties dialog box is displayed.
- Select Plot Lines of Constant Z. Deselect the Plot Lines of Constant X and Plot Lines of Constant Y. Click OK to accept the remaining default parameters. A wireframe map based on TUTORWS.GRD is drawn.
- Press CTRL-A, or choose the Edit | Select All command, to select both the vector map and the wireframe map. Choose the Map | Overlay Maps command to overlay the two maps.
- If you want the map to fill the window, choose the View | Fit to Window command. The view of the map is magnified so the map fills the entire plot window.
The vector map showing the local gradients is plotted overlaying a wireframe map showing lines of constant Z.
