Curve maps are bundles of curves measured in points of a regular grid. While the grid is regular, like in image and volume data, curves in each bundle can have different numbers of points. Some bundles can even be empty (no data were measured in the corresponding point). Curve maps also usually comprise several data series, for instance height and force, whereas in other types of data each physical quantity is a separate data item.
Containing a bundle of curves in every point means that also the independent variable is one of the curves. For example, the force-distance curve bundle contains the force values and distance values. In most of the modules using curve maps one needs to choose which variable is dependent and which independent (sometimes the module can guess it).
An important concept is also the segmentation of the curve bundles. In some cases it is useful to have some marks on the bundle, e.g. to separate the approach and retract part of a force-distance curve. Such marks form segments which are then used by data processing modules. Segments are individual to curve bundles, so each bundle can use only one set of marks. Segments can be loaded from manufacturer's file format, or created in Gwyddion.
Button z direction (minimum, maximum, mean, …), or alternatively just any two-dimensional data of the same dimensions can be shown as the preview.near the top of the window can be used to change the preview image. The preview can either be calculated as a summary quantity for one of the curves characterising data along the invisible