Raymarine GPM400 Reference Manual page 27

Panning and zooming
In the appropriate application windows, you can pan and zoom the
view to display a different geographic area (pan) or change the
scale at which an area is displayed (zoom).
Panning
In the chart, 3D chart and weather applications, you move the cur-
sor using the trackpad. When the cursor reaches an edge of the
screen, the view automatically pans to display the appropriate area.
Zooming
In chart, 3D chart, fishfinder, weather or radar windows, you can
use the Range In / Out rocker switch to change the scale of the
view. When you zoom in, you see a smaller area of the chart in
more detail (large scale). When you zoom out, you see a greater
area of the chart in less detail (small scale).
The level of cartographic detail available at different scales varies.
Some charts provide detail at smaller scales than others.
If you select a chart scale that does not provide cartographic detail
for your chosen area, the chart will use the most detailed level
available for the surrounding area and stretch it to fit the selected
scale. This means that you will never have blank or hatched areas
on your screen. However there may be some mis-alignment of
objects which cross the chart boundary in this area.
Chapter 2: Operating Principles
27