Houston, Texas July 1997 The city of Houston is the fourth largest city in the United States. Houston is a port of entry and has the second busiest port in the United States. The city is a major financial, commercial, manufacturing, and transportation center in the southwestern United States. Houston boasts one of the worlds most comprehensive and competent medical centers. The city is located on a delta that was formed during the end of the last ice age some 6000 years ago. Numerous Interstate Highways and other major transportation routes are visible traversing through and around the city. The runways of the George Bush Intercontinental Airport are discernible midway between the center and the top center of the image. Just to the right (east) of the airport, the sediment-laden waters of Lake Houston can be seen. A small part of upper Galveston Bay is visible in the lower right portion of the image