Items which do not have real world sizes on the map (cartographic artefacts such as text, Symbols, LineString thicknesses and hatching patterns) need to be scaled differently from real world items (roads, buildings, etc.). To deal with this, each dataset has a Dataset Scale.
Point text does not exist as a geographical feature, it is simply stored as a position. The height of the text might be set to 12 points (approximately 1/6th inch or 4mm high). Imagine viewing the North American continent with the state names printed in 12 point text! It would take a spy satellite to read the names, or you would have to zoom in very, very closely!
By setting the Dataset Scale to an appropriate value, Text, Symbols, LineString thicknesses and hatching patterns will be displayed appropriate to that scale. A map of the states of the USA would need a Dataset Scale of about 1:20,000,000 for the 12 point state names to appear at a reasonable size. In other words, display 4mm text at a height of 4mm x 20,000,000 = 80km high!
To change the Dataset Scale select Overlays [Home-Map], click on the Dataset tab and enter the required scale in the Scale box. However, if the dataset is read only this will not be possible. For this reason SISprovides you with the ability to override the Dataset Scale with an Overlay Scale (see below).
Dataset Scale can also be changed by right-clicking on the overlay in the Maps Control Bar, selecting Dataset > Properties and entering the required dataset scale in the displayed dialog.
Different datasets in an SWD can have different scales, therefore you could overlay maps at a scale of 1:1250 with maps at 1:10 000. Some external file-based datasets know their dataset scales (e.g. Ordnance Survey MasterMap Topographic layer is automatically set to a scale of 1:1250).
When you create a base dataset file or an internal dataset, they take their Dataset Scale from the first overlay that has been opened. If the first overlay is, for example, the GB National Grid backdrop, which has a scale of 1:10000000, the scale of your new dataset will also be 1:10000000. If there are no overlays open (i.e. it is a new SWD), the Dataset Scale will be set to 1. If you wish to alter the Dataset Scale, you can do this in the Overlay dialog, Dataset tab.
The scale of any dataset can be overridden using the following method:
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