Zoom Ranges

The zoom range is a property of projected drawings and other components that appear in maps. It specifies the zoom levels in which a component is displayed in a map. For zoom levels outside the specified zoom range the component will automatically be hidden from view. The zoom range mechanism therefore makes it possible to create maps where dense components are not seen when the view is zoomed far out and where the component is displayed when zooming far enough into the map.

Zoom ranges are set within the native type of component window, but they become operational only when the component is displayed in a map window. Zoom ranges are not set by clicking on the layer's tab in a map window. They are set by opening the layer in its own component window and then choosing View - Properties - Zooms.

To set zoom range, open the component in a window (for example, open a drawing in a drawing window) and choose View - Properties and then click on the […] button to the right of the Zooms caption to open the Zoom Range dialog.

images/dlg_zoom_range.png

By default the From and To ranges are Any. This means the component will be visible in maps at any zoom level. We can choose preset zoom values in factors of ten from 1:1 to 1:1000000000 as well as Any and Custom in the list boxes. The Current Zoom number shows the current zoom in the opened drawing window. It will vary as we zoom in or out of the window. It has no effect in setting zoom ranges except to provide a guide that may be used to estimate which zoom values to enter in the From or To boxes based on the current appearance of the component window.

images/dlg_zoom_range_01.png

If we set the To range value set to 1:10000 the component will be visible at all zoom levels up to 1:10000 after which it will not be displayed in maps.

images/dlg_zoom_range_02.png

Choosing Custom in the To or From range boxes activates the controls to the right of the From or To box. This allows us to enter a custom zoom range. For example, if we enter Custom in the To boxe we could enter a zoom of 1:5000.

This setting of zoom range means that the component will be hidden in maps at zoom levels farther than 1:5000. As we zoom in to zoom levels between 1: 5000 and 1:1000 the component will be shown in maps. When we zoom in below 1:1000 the component will again be hidden.

Very Important: Although the zoom range is set when the component window is open, it has an effect only when the component is displayed within maps. Also, zoom ranges can only be set on projected components. They cannot be set for components in Latitude / Longitude coordinates.

See the Turning Layers Off/On by Zoom topic for an example.

Comments

Why are zoom ranges not used in Latitude / Longitude maps? The reason is that such maps use geographic degrees as their unit of measure. Unlike meters or other linear measures used in projected coordinate systems, the size of a degree is different depending on its location on Earth. Degrees near the Equator are sixty nautical miles "wide" (their extent in longitude) but degrees very near the North Pole are only a few meters wide.

Because the size of a degree varies, any scale factor expressed in degrees also varies. If zoom ranges were allowed to apply in maps using Latitude / Longitude, one could have components appear and disappear in maps not as a result of zooming in or out but simply as a result of moving Northward along a particular meridian of longitude.

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