A good source for a map of the San Antonio River Walk is available at thesanantonioriverwalk.com, described as "The Official Website of the San Antonio River Walk." There is a link at the site's home page to River Walk maps.
To view and download maps, scroll toward the bottom of the home page for the link to River Walk maps. There are maps for the River Walk in downtown San Antonio as well as a map of the entire park. Each map comes up as a PDF file. The downtown map shows various points of interest, such as tourist destinations, hotels, restaurants and other businesses along the River Walk and close to the park. The complete map includes streets around the River Walk and also shows the number of miles both north and south of the center of the River Walk along with many points of interest in San Antonio.