Ciudad Juarez, across the US-Mexico border from El Paso, Texas, supports a population at least 1,300,000 people. On the U.S. side of the Rio Grande, El Paso is marked by the brightly-lit Interstate Highway I-10 that cuts across the city. Although the area of El Paso, with an estimated population of slightly more than 600,000 is roughly on the order of the area of built-up Ciudad Juarez, the density of settlement, evidenced by the distribution of lights, is much less.