Sperry Marine Visionmaster FT ECDIS, User Manual

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Charts ECDIS User Guide
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Compilation Scale
Chart data is compiled at a specific scale, based upon the hydrographic
data from which the chart was created. This scale is called the chart’s
compilation scale, indicating the level of detail that is available on the chart.
When charts are first selected for display, they are displayed at their
compilation scale.
A chart's compilation scale is shown in the drop down list of the Charts
button (see Chart Database & Sub Menu Selection in Chapter 3), the
Detail tab folder of the Legend menu, (see Legend Detail) under Chart
Usage/Scale, and Chart Index, which shows the scale and other details of
all charts in a selected chart database.
When the scale ratio is selected at a larger scale than the chart's
compilation scale a permanent prompt appears with the message `Primary
Display Overscale', see `Chart Overscale’ below.
Navigational Purpose
In addition to the compilation scale, the level of detail and expected
accuracy available on a chart is also related to its navigational purpose. For
example, Harbour, Approach, Coastal or General. A vector chart's
navigational purpose is shown in the Detail tab of the Legend sub menu,
(see Chart Legend Detail) under Chart Usage/Scale. The navigational
purpose of all charts is shown in Chart Index (Usage Level) (see Chart
Tools).
Chart Overscale
There are three ways in which the system indicates that
chart data is being displayed at a larger scale than its
compilation scale: the Display Overscale Prompt
(detailed in Prompts), the Display Overscale Pattern (detailed below) and a
permanent indication in orange lettering at the top right of the chart display,
below the Watch mode button.
Display Overscale Prompt
The prompt appears as Primary Display Overscale or Secondary
Display Overscale , depending on the current display option, see Primary
and Secondary Display Options.
The display overscale prompt appears when any of the following three
conditions are met: