US POPULATION DENSITY CHANGE MAP HOW TO

US POPULATION DENSITY CHANGE MAP HOW TO

One of the questions that remains to be answered is how to deal with population changes over time. There are several potential improvements under consideration for the process. A drought that covers an area with a population of 15 million people is most likely going to have a different impact than a drought that covers an area of 500 people. The purpose of these numbers is to give an idea of the magnitude of the number of people living in a drought-stricken area. Again, this is simply due to the way that the numbers are calculated and should be interpreted that the USDM category in question is basically non-existent in the area. For example, it might be possible that the calculations determine that 5 people are living in the area of a USDM category. For example, instead of using an exact figure of “1,026,493 people” it would be better to say “more than a million people.”ĭue to the way the numbers are calculated, there are also instances where the numbers don’t seem logical. It is up to the user to determine how much rounding should be necessary for a given purpose. The numbers are presented with a high degree of precision due to the calculation process, but should be considered artificially precise. And a lack of mountain snow can affect the water supply for cities hundreds of miles away.Īny population figures provided should be considered a rough estimate. For example, a drought in a major agricultural region might increase food prices even in areas that aren’t in drought. Drought can affect people living outside of the areas it is directly affecting.The observations and experiences of people in an area labeled D2 may not differ meaningfully from the experiences of people in an area labeled D3. These areas should be considered more of a transition zone. The USDM boundaries are considered “fuzzy.” For example, this means that the magnitude of the drought does not necessary change drastically along the boundary between D2 and D3.For the purpose of these calculations, it is assumed that the population of an area has not changed since the last census was taken. Population is fairly fluid and real-time population numbers for an area are constantly changing. The population of an area is not static for long periods of time.We assume that population is distributed evenly across each county, although in reality, it isn’t.There are several assumptions made in order to simplify the calculation process, necessary to ensure that the numbers can be available when the map gets released each week. Caveatsĭue to the fact that there is quite a bit of estimation throughout the process, these numbers are not exact values. The state values are then aggregated to the national level. Once the county-level statistics are calculated, the numbers are aggregated up to the state level by summing the values for each county within the state. To compute the population in drought statistics each week, this population density value is multiplied by the percent of the area in a given USDM category to determine the number of people living in the area of each USDM category.

The population density for each county was determined by dividing the population of the county by the area of the county in square miles. Census data, which is collected and distributed every 10 years. To calculate the number of people living in areas that the USDM classifies as being in drought, we use the most recent U.S. Below is an explanation of how these numbers are calculated and how they should be interpreted. The National Drought Mitigation Center provides estimates of the number of people living in areas affected by drought.

Us population density change map