SMSA's as exclusion areas would be misleading since large portions of these counties are not urbanized. Therefore, certain alterations were made to these defined SMSA's. Alterations were made by examining a "dot" map of population distribution, prepared by the Department of the Census from 1970 Census data, and eliminating grid cells from the SMSA that were indicated as having less than 500 people. Spatial Coverage: Areas indicated as SMSA's on Figure 7 include 1871 grid cells across the United States. 2. Population Density Greater than 50 Persons per Square Mile Rationale: As discussed previously, populated areas other than SMSA's need to be represented. A second type of indication is a population density analysis, and areas that were identified as having a population density greater than 50 persons per square mile were mapped and considered as exclusion variables. Reliability of the Data: The areas mapped as having a population density greater than 50 persons per square mile were compiled from a map prepared by the Department of Census from 1970 census data. Therefore, the information represented by this variable is somewhat out of date. However, a more severe shortcoming of the data relates to the fact that the data was represented on a county by county basis. Although counties are commonly used for data representation purposes, the land area represented by many counties causes significant concentrations of people to be diluted when the data is mapped on a county by county basis. Therefore, while there is a great degree of confidence that the mapped information is an accurate representation of those counties with a population density greater than 50 persons per square mile, there are many areas of the United States that are not adequately represented through the use of this population variable. Spatial Coverage: The land area represented as having a population density greater than 50 persons per square mile include 1276 grid cells. It should be noted that this count does not include the areas previously mapped as SMSA's.
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