Using Zoom Scale

When you open image data, it displays at a specific scale; for example, 1:150 000. You can set up Zoom Scale to activate a layer of imagery in a resolution range you specify. By doing so, the image becomes visible only when the viewing resolution is between the minimum and maximum values set for that layer. When the current viewing resolution is outside the minimum and maximum range, the layer is not visible.

Using Zoom Scale can be very useful when viewing both high-resolution and low-resolution imagery of the same area. For example, suppose you have a 30-meter Landsat image, a 10-meter SPOT image and 1-meter aerial photo, each covering the same area. You can view the Landsat image in the view pane, but the aerial photo cannot be used, because its pixels are too small to render an accurate image. Conversely, when you zoom in on a ground feature using the aerial photo, the Landsat and SPOT scenes cannot be used because their pixels are too big.

By setting up Zoom Scale, you can use it to deactivate the Landsat image when you are zoomed in on the aerial photo, but deactivate the aerial photo when you zoomed out on the Landsat scene. The following table shows the settings to use for the preceding example.