Chicago Grid (IMAGE) Penn State Caption This graphic shows overlapping land areas the researchers used to estimate the effective population in relation to the land base within a specified radius from the center point of Chicago. Credit Christine Costello/Penn State Usage Restrictions non commercial use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.