I don't believe the maps are being used to pinpoint the exact location, but are added as a tool for the reader to use to help THEM locate the area. Try the zoom out, zoom in and click and drag features of the map, put forth some effort and don't expect everything to be handed to you.
Those maps are just thrown in for laughs, I think. They rarely go with the story.
Unless, you mean highway 77 and higway 59 in victoria county, which is not what your map indicates here
Highway 77 does not run through Goliad County...
its 183....or 77A, but not highway 77