Keep in mind that this only applies to statutorily prohibited locations. It does not apply to private property that is posted with valid 30.06 signs. Private property owners can post their entire property if they wish, parking lots and all.
Look on page 40 of your Texas Concealed Handgun Laws book. At the bottom of the page it list Premises as "a building or portion of a building. The term does not include any public or private driveway, street, sidewalk or walkway, parking lot, parking garage, or other parking area". Yes this is a quote, I suggest you carry your book in your car, I plan to.