Numeric data

Contrary to nominal and ordinal maps, the numeric map reveals the quantitative character of collected data. Regarding numeric map information, we have to consider two different types of data: Interval and Ratio data.

Interval data

The interval level of collected data have three characteristics:

The categorisation of data
The ordering of data, but with...
...explicit numerical indication of the categories value

Interval example

Interval Data Example, Atlas of Switzerland 3 (Bundesamt für Landestopografie swisstopo (eds.) 2010)

Example: Temperature in Switzerland (mean annual temperature 1961-1990, degree celsius). A classic example for interval data is the temperature scales of CELSIUS and FAHRENHEIT. Both scales consist of ordered values and reveal the precise difference between their temperature values. However, the problem of these interval scales is the arbitrary character of their zero points.

Ratio data

Ratio data has the same characteristics as interval data:

The categorisation of data
The ordering of data, but with
The explicit numerical indication of the value differences between the categories.

However, contrary to interval data, ratio data has no arbitrary but an absolute zero point. In many fields, it is very common to work with ratio data.
Continuing with the example of temperatures, we state that the KELVIN scale has an absolute zero point and therefore has a ratio scale. This absolute zero point of temperature is the lowest possible temperature of anything considered in the universe. Thus, we are allowed to say that 30°K is twice as warm as 15°K, also in terms of kinetic energy of molecules (Slocum 1999).

Ratio example

Ratio Example, Atlas of Switzerland 1 (Bundesamt für Landestopografie swisstopo (eds.) 2000)

Example: Precipitation in Switzerland (average April, in mm). The registration of precipitation has an absolute zero point too. If there is no rain falling, we measure 0 mm of precipitation. So we can say that 1000 mm is twice as much as 500 mm because precipitation relies on ratio data.