Sample size (n) refers to the number of participants or observations included in a study through which statistical inferences for the whole population are made. Can sample size have measurement unit, such as $km^2$ (kilometre square)?
In a paper on hydrology, researchers collected data from some areas, but they didn't specify the number of areas, rather said they collected the data from a area of size $20km^2$. Is this $20km^2$ the sample size in the study? I didn't find any other information in the paper which can be potential as a sample size.