Introductory Notes

Sources of Data: The topographic transects were constructed from data collected in the field by Dr. Malmström and his student assistants; climatic data were obtained from World Weather Records and the Secretaría de Recursos Hidráulicos; most statistical data were derived from recent publications issued by the Instituto de Estadística, Geografía, e Informática (INEGI).

Presentation of Data: A variety of types of maps are employed in portraying the data shown in the following pages. Symbol maps depict data in the form of squares proportional to the amount of a given item in each political entity -- usually a state. Choropleth maps show gradations in data in increasing intensities of color, ranging from yellow at the lower end of the scale to red at the higher end. On most of the choropleth maps, the data is (1) either scaled in quartiles (lowest quarter, next lowest quarter, next higher quarter, and highest quarter) according to the range of data found within the country as a whole, or (2) according to specifically designated thresholds, such as .75, 1.00, and 1.25. Yet other choropleth maps are scaled according to the "Location Quotient", which sets a value of 1.00 for the country as a whole and then compares the relative distribution of an item in each political entity against that; thus, a state with an LQ of .5 has only half as much of an item as the national average, while one with an LQ of 1.25 has a quarter more of a given distribution than the average for the country.

Navigation Through the Atlas: At the bottom of each page, the reader is provided with an active link to the current topic of interest and/or to the Table of Contents.