You may have noticed when you are zoomed in closely on Ordnance Survey NTF data, all graphics are visible, but as you zoom out, graphics and text progressively disappear. This is designed to speed up the display of very complex maps. Imagine zooming out to see all graphics on five hundred detailed maps, displayed on a 17" computer screen - the display would be a solid blob of colour.
All graphics in NTF files are tagged by Ordnance Survey with a Feature Code, which is a number indicating the type of feature it represents. Building outlines have the Feature Code 1, and are generally fairly small items on a map, while Road Centrelines have Feature Code 98, and are key features at almost any screen scale. To display every Building Outline when looking at 50km² would normally be inappropriate, whereas to display Road Centrelines is very useful.
For this reason, SIS filters out certain features when the screen display scale becomes too small.
You can use scale filters for your own graphics by setting the minimum and maximum scale threshold properties of editable items (Minimum scale and Maximum scale).
If you want to change the scale filtering of read-only data like Ordnance Survey NTF then you can either edit the Feature Table, or force the scale thresholds using Overlays [Home-Map].
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