Size dimensions give the width, length, and depth of the object. Location dimensions tell edges. Chain dimensioning is where the length of one side is determined from one point connected to another, then the other point connecting to a different one, and so on. Datum dimensioning is where all measures are determined from one point on the object. Datum dimensioning is most likely the more common practice of dimensioning since there is only one point to base the data off of, so it will be more accurate. Dimensioned drawings and descriptions both describe the object.