Interpolation
Also called: Spatial interpolation · Topic: Graphical Representation of Data and Thematic Maps · NCERT: Class 12, Ch 3 "Graphical Representation of Data"
Meaning
Interpolation means estimating values between places where readings were actually taken. It assumes the value changes evenly with distance. It is how isopleths (lines joining places of equal value) are drawn from scattered station readings. NCERT's formula is: position of the isopleth = (distance between the two points ÷ difference between their values) × interval. In GIS (computer mapping), methods such as inverse distance weighting and kriging do this automatically. IMD uses them to turn rain-gauge and weather-station readings into gridded rainfall and temperature maps.
Example
In NCERT's example, two stations reading 28°C and 33°C are 10 mm apart on the map. The 30°C isotherm falls (10 ÷ 5) × 2 = 4 mm from the 28°C station.
Don't confuse with
- Extrapolation estimates values outside the range of the known points. Interpolation stays between them.