Is there a difference between plottage and assemblage?

From the IAAO's "Property Assessment Valuation" - 2nd edition

"Assemblage and Plottage Two terms commonly confused in appraisal terminology are assemblage and plottage. Plottage is the combining of two or more sites under a single ownership in order to develop one site having greater utilityand unit value in the aggregate then when each is separately considered. Assemblage, on the other hand, is simply the merging of adjacent properties into one common ownership or use. Generally, when the new site has a greater utility than the sum of the old sites, the new site will have increased value. This value increment is is known as plottage value. Occasionally the assemblage of land will result in the creation of a new site with less utility, which normally would result in a lower value. This value decrease is known as negative plottage"