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Wasmer Consulting - NMPlot - User's Guide - Changing the Plot Background


NMPlot User's Guide, Chapter 13: Changing the Plot Background

NMPlot gives you considerable control over the background of a plot. It can be as simple as a solid color, or as complicated as a set of map layers displaying themes such as roads and rivers. The background can also include plot elements, such as contours and geographic annotations, from other girds. This allows you to overlay contours from two or more grids.

Background Color

When NMPlot draws a plot, it first fills the entire plot with the background color. To set the background color, follow these steps.

  1. Go to the Background Color page of the Plot Options dialog box.

  2. Background color: Select the background color. See Color Control for information on selecting colors.

Background Layers

You can add any number of background layers to a plot. Use Map Background Layers to display background maps. Use Grid Overlay Background Layers to overlay contours from two or more grids.

Managing Background Layers

Use the Background Layers page of the Plot Options dialog box to manage background layers.

Check the Show background layers box to display background layers. If this box is not checked, no layers will be shown.

The background layers list displays all background layers. This list is presented using a spreadsheet control. See Spreadsheet Control for more information.

Adding a Background Layer

To add a background layer, follow these steps.

  1. If desired, select an existing layer by clicking on it. The new layer will be added just before the selected layer. Ignore this step if the list is empty.

  2. Press the Add Layer button, located below the background layers list. The Select Layer Type dialog box is displayed.

  3. Choose the type of layer you would like to add, then press OK. As a shortcut, simply double-click on the desired layer type.

    The Grid Overlay layer type is described in Overlaying Grids. The background map layer types are described in Background Map Formats.

  4. A new layer, of the appropriate type, is added to the list.

  5. Press the new layer's Options button. The layer's options dialog box appears. Set the layer options as desired.

Removing a Background Layer

To remove a background layer, follow these steps.

  1. Select the layer to remove by clicking on it in the background layers list.

  2. Press the Remove Layer button, located below the background layers list.

Ordering Background Layers

Background layers are drawn in order, starting with the last layer in the background layers list. This means that the topmost layer in the list is drawn last, and therefore appears on top of other layers. Generally, you will want to order the list so that the most important layers are at the top.

Note:

Background layers are drawn in three stages. All area features are drawn first, followed by all line features, and finally all point features. This means that a filled area feature will not obscure a point feature, regardless of the ordering of the layers. This matches most people's intuitive idea of how layers should work.

To change the ordering of layers in the list, follow these steps.

  1. Select a layer by clicking on it in the background layers list.

  2. Press the Move Up In List or Move Down In List button to move the selected layer. These buttons are located just below the background layers list.

    If you press and hold one of these button, it will automatically repeat. This is useful for moving a layer several rows up or down.

Hiding or Displaying a Background Layer

Use the Show column of the background layers list to selectively hide or display individual layers. A layer will be displayed only if its Show box is checked.

Changing a Background Layer's Options

Use the Options column of the background layers list to change the options used to display a layer. Pressing a layer's Options button will display that layer's options dialog box.

Overlaying Grids

Using Grid Overlay background layers, you can overlay the plot elements from two or more grids. For instance, you can create a plot that displays contours from two different grids. This is useful for comparing grids representing alternative scenarios.

As an example, assume that you have two grids. The first represents the existing noise levels around an airport, while the second represents the predicted levels a few years in the future, after air traffic has increased. You create a plot that displays both the current and predicted noise level contours. This plot clearly shows how far the noise contours are expected to grow. See the sample plot included with NMPlot, Sample Plot - Contour Overlay.nmp, for an example.

To create a plot overlaying two grids, follow these steps.

  1. Create a new plot, and set its primary grid equal to the first of the grids you want to overlay.

  2. Add a new Grid Overlay background layer to your plot. See Background Layers for instructions.

  3. Click on the new layer's Options button. The Grid Overlay Options dialog box appears.

  4. The Grid Overlay Options dialog box looks very similar to the Plot Options dialog box. In fact, with the exception that some pages are missing, it is nearly identical. Set the options for the overlay just as you would set the options for a regular plot. Set the overlay grid (which is the Grid Overlay's equivalent to a plot's primary grid) equal to the second of the grids you want to overlay.

    Note:

    The missing pages on the Grid Overlay Options dialog box contain options that are not applicable to an overlay. For example, the Plot Orientation page is missing, as it is nonsensical to have the overlay oriented differently than the main plot.

Tip:

You can overlay as many grids as you wish. Take care, however, as overlaying more than two sets of contours can result in a cluttered plot that is difficult to interpret. A plot overlaying contours from several grids works best if you make one set of contours very bold (use thick, solid lines in a dark color), and make the rest of the contours more subtle (use thin, possibly dashed lines in lighter colors).

Displaying Background Maps

NMPlot can display your plot over one or more background map layers.

The map layers can be stored in a number of common Geographic Information System (GIS) formats. These formats are discussed in detail in Background Map Formats.

To add a background map to your plot, simply add a new background layer of the appropriate type, as described in Background Layers. See Background Map Formats for instructions on setting the layer options associated with each map format.


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