Geographic Information Systems: An Introduction, 3rd Edition

11.3 Resolution and Sampling Rate

Spatial resolution refers to the minimum size of objects that can be registered. In practice, spatial resolution has been closely linked to map scale—large map scale gives high resolution and small map scale gives low resolution. Sampling rate refers to the pattern of density in space or time of the observations. Normally, resolution and spatial sampling rate will coincide, but in principle they are different. For example, in raster data one can have small pixels (high resolution), but with greater distance (low sampling rate) (Figure 11.6). Vector data can have small objects that are observed/described with one or few points. In raster data the observation unit (cell size) selected can be too large to register all the objects desired (Figure 11.7).

Normally, low resolution gives poorer accuracy than high resolution, because observations with low resolution usually do not have the same closeness to the “true” values as observations with high resolution. The importance of resolution is particularly visible in relation to areas: Low resolution gives generalized and greater areas, whereas high resolution gives smaller areas. In raster data resolution normally refers to pixel size—for example Landsat TM with a resolution of 30 m, and SPOT Pan 10 m.

In GIS attributes can also be described as resolution. For quantitative attribute data, resolution is determined by the precision of the measuring instrument, and for qualitative data it is determined by ...