population density -- 2

The file [login to view URL] (distributed with the project files) contains real data published by the U.S. Census Bureau. The data divides the U.S. into 220,333 geographic areas called "census-block-groups" and reports for each such group the population in 2010 and the latitude/longitude of the group. It actually reports the average latitude/longitude of the people in the group, but that will not concern us: just assume everyone in the group lived on top of each other at this single point. Given this data, we can imagine the entire U.S. as a giant rectangle bounded by the minimum and maximum latitude/longitude of all the census-block-groups. Most of this rectangle will not have any population: The rectangle includes all of Alaska, Hawaii, and Puerto Rico and therefore, since it is a rectangle, a lot of ocean and Canada that have no U.S. popluation. The continental U.S. is not a rectangle. For example, Maine is well East of Florida, adding more ocean. Note that the code we provide you reads in the input data and changes the latitude for each census group. That is because the Earth is spherical but our grid is rectangular. Our code uses the Mercator Projection to map a portion of a sphere onto a rectangle. It stretches latitudes more as you move North. You do not have to understand this except to know that the latitudes you will compute with are not the latitudes in the input file. If you find it helpful to do so, you can change the code to disable this projection during your testing. We can next imagine answering queries related to areas inside the U.S.: For some rectangle inside the U.S. rectangle, what is the 2010 census population total? For some rectangle inside the U.S. rectangle, what percentage of the total 2010 census U.S. population is in it? Such questions can reveal that population density varies dramatically in different regions, which explains, for example, how a presidential candidate can win despite losing the states that account for most of the country's geographic area. By supporting only rectangles as queries, we can answer queries more quickly. A different shape can be approximated using multiple rectangles, but this is "Above & Beyond." Your program will first process the data to find the four corners of the rectangle containing the United States. Some versions of the program will then further pre-process the data to build a data structure that can efficiently answer the queries described above. The program will then prompt the user for such queries and answer them until the user chooses to quit. For testing and timing purposes, you may also wish to provide an alternative where queries are read from a second file. We also provide you a graphical interface that makes asking queries more fun.