The map on the bottom left indicates population density in the U.S. in the year of 2000. The color ramp includes shades of blue. Navy blue is the darkest color indicating the most dense areas. The lighter color of blue represents areas that are less dense. The color would be darker for the areas that are denser in population. The population density is calculated in units of people per square mile. A field calculator is used in ArcMap to calculate the values. The number of people in the year 2000 is divided by the area of the country. In other words, the population density is calculated based on the number of people focused in a specific area. In this case, the number of people in U.S. is considered.
The top right map indicates percent change in the U.S. for the year of 1990-2000. The color ramp includes two shades of color, purple and yellow. Purple indicates an increase in percent change. Purple is darker for the population that has the greatest percent change. Lighter shades of purple is used for percent change that is not as great. Yellow represents negative percent change in the population. More negative percent change has darker shades of yellow.
The bottom right map indicates the number of people in the U.S. for the year of 1990-2000. Shades of purple is chosen for the color ramp. The symbols are flipped and sorting is reversed, as it is for the first three maps. So, darker purple specifies a higher number of people in the U.S. in 1990-2000. A less populated area is displayed with a lighter purple. It would be confusing for the reader to determine which areas are more populated if higher populated areas are marked with lighter shades of purple. It is more relevant and logical to color the higher populated areas with darker colors.
These maps have some major cartographic design problems. First, the assignment asked you to zoom into the lower 48 states, so that the map would be easier to read. Second, at such a large scale, the colors of the census tracks are barely visible because the borders of them are so large. Finally, if you were to go with the large extent that you did, you ought to adjust the layout to landscape view so you can fit more on the page.
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