Why do you use kilometers?
Because it is a sensible unit for measuring distances. It can be related easily to smaller units of distance - like a metre. And there are many crossovers to other measurement units in the SI system - for mass, force, etc.
The use of meters instead of kilometers is too small a comparative scale for astronomy, and suggests an accuracy that is not always present. The distances are expressed in hundred of thousands or millions of kilometers, so often even larger units such as the Astronomical Unit (AU, about 150 million kilometers) or parsecs (about 30 trillion kilometers) are used to compare values.
According to Food and Agricultural Organization (FAO) figures for 2007 on WorldStat website, arable land and agricultural land account for 20 square kilometers each in Aruba's land use. Specifically, Aruba's total area amounts to 180 square kilometers. Forest area accounts for 4 square kilometers. The category of "other" accounts for 156 square kilometers.