Two measurements can use metres while describing completely different directions. A 12-metre dinosaur body length is not a claim that the dinosaur stood 12 metres tall. A clear comparison names the dimension before it draws the objects.
Height measures a vertical dimension
For a person, a height is measured from the feet to the top of the head. For a landmark, the answer may include an antenna or spire. For an elephant, shoulder height does not include a raised trunk. Each library entry tells you which definition was chosen.
Length measures the specified long direction
A whale’s total body length includes the tail. An aircraft’s overall length measures the fuselage from front to back. Neither is a measure of standing height. The blue whale and A380 comparison uses length for both objects.
Diameter is the width across a circular body
The diameter of a ball runs through its centre. Its circumference travels around the outside. For a sphere, circumference is pi times diameter. That is why an equipment specification given as a circumference needs a conversion before it can determine a drawing’s width.
Planets are not perfect spheres. NASA publishes both equatorial and mean diameter figures in different resources. SizeGuess labels the convention so the Jupiter and Earth comparison uses a consistent equatorial definition.
Elevation is a reference to sea level
A mountain’s summit elevation is the altitude above sea level. It is different from the height above a local valley or the mountain’s geological base. In the Nature collection, summit elevations are explicitly labelled. The mountain icon is schematic and does not depict a measured hillside profile.
The measurement methodology explains how one metres-to-pixels scale supports comparisons between different axes.