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 for this purpose. The result, of course, misrepresented the legal geography of Puerto Rico, and therefore did not provide data users with statistics that reflected the true boundaries of the legal entities. This distortion of the legal boundaries had been made for one area—Arecibo—for the 1960 census.

In order to make the decennial census data more useful for statistical analysis, there was a need for a geographic entity that would better represent the urban development centered on the seats of municipio government. To fill this need the Census Bureau asked the Puerto Rico Planning Board to delimit the urban core population of each municipio. The Planning Board suggested that the Census Bureau call these areas zonas urbanas (literally translated as urban zones). Identification of these separate place entities left the underlying MCD structure intact so that data would be available for both the legal MCDs and the statistical places.

Areally, every zona urbana is equal to or larger than the barrio-pueblo that forms its core. Because, by the Census Bureau’s definition, there are no incorporated places in Puerto Rico, the zonas urbanas, together with the aldeas (discussed later), serve the statistical function of places, equivalent to CDPs in the United States. The zona urbana boundaries are drawn to follow visible features and/or the limits of a municipio or barrio. The boundaries of zonas urbanas may be revised for each decennial census as the built-up area changes, except that they may not extend beyond their municipio. There is no minimum population requirement for an area to qualify as a zona urbana.

The term zona urbana can be the basis for confusion, because the Puerto Rico Planning Act identifies a second type of zona urbana: a quasi-administrative area, delineated by the Planning Board, that is subject to land use controls and is eligible for designation for government grants. Furthermore, the term zona urbana is used in some documents to refer to the area that the Census Bureau previously had identified as the ciudad. In addition, the similarity of the designations zona urbana and área urbanizada (urbanized area, or UA) tends to confuse even those familiar with census geography. UAs represent a population concentration of at least 50,000 inhabitants; the Puerto Rico and the Outlying Areas7-35