Missions tended to be located near running rivers or larger streams. They also tended to choose areas with larger flat areas that would be good for farming. Farming was important as this would be one the main ways that the missionaries fed themselves and what they taught willing Native American converts. Missions appear during the time when we had to adapt and adjust to the environment around them. They didn't have the ability to adjust the environment to their needs.
Resources determine where people live, the kinds of houses that they build, and how closely they live together. The missions were built in the most favorable locations where resources were readily available.
