An indicator is a visible or empirically measurable quantitative characteristic (ratio), of some spatial feature, term or process that is not immediately accessible yet of particular interest to experts in the fields of geography, spatial planning and environmental research. Indicators have to be formalized and evaluated in terms of concrete spatial reference units to enable their wider application and cartographic illustration. The geospatial interpretation of indicators provides insight into related aspects of spatial structure or processes with a spatial dimension.

The function of indicators in the fields of spatial planning and urban development are to communicate the level of progress towards specific goals as well as the results of spatial surveys and measurements. They must therefore possess the following characteristics: conformity with stipulated goals, significance, comprehensibility, spatial comparability and practicality.

Indicators help to identify the various stages of progression towards agreed goals. They signalize improvements or setbacks as well as requirements for action. Spatial indicators permit comparison of diverse regions or cities and can identify gaps in the existing data set.

More narrowly, ratios can be employed as indicators to provide answers to specific questions (for example: the parameter "proportion of surface water to total area" can give be used to calculate the numbers of waterfowl in a reference area). Thus for purely practical reasons the Monitor of Settlement and Open Space Development does not make a clear distinction between ratios and indicators.

IOER Monitor Indicator Calculation

Ratios and indicators are automatically calculated in a geo information system (GIS). The geo base data is extensively processed beforehand. Manual sampling and partly-automated checks using the same base data provide assurance of quality. However, it is impossible to confirm or exhaustively check for complete accuracy of results.

Indicator values are withheld when these are obviously implausible. Extreme values and large jumps in values are clearly marked following an evaluation of the geo base data (e.g. reclassification of large areas with no visible changes in land use). In addition, parameters which display unjustifiable disparities due to the diverse forms of data capture by the individual states are not published (e.g. proportion of combined use areas in built-up areas).

Geo base data is generally not corrected in any way; however, any discrepancies discovered in data sets are passed on to the state surveying agencies or the Federal Agency for Cartography and Geodesy (BKG).