The pica is a unit of length in the field of typography and uses the symbol pc.
There are 12 points in 1 pica. 1 pica represents approximately 1/6 of an inch.
Picas are expressed using numbers and a lower case p on software such as Adobe InDesign - for example 8p6 which would represent 8 picas and 6 points (or 8.5 picas).
The Pica is very useful in measuring and calculating the space needed to print letters and words on paper - for example when laying out books or magazine articles; the font lengths are quanitified by the number of characters per pica (cpp).
The kilometre is a unit of length and is a multiple of the metre; an SI derived unit. It has the symbol km.
A kilometre is equal to 1000m, 1094 yards and 0.621 miles.
Kilometres is used to measure road distances in the US, though the UK is still using the imperial "sister" miles.