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Understanding Maps, Topography, and Historic Aerial Photos


If you have land that you want to manage, having and understanding maps of your property is crucial to achieving better management. However, many different maps provide you with different information about your land; which ones should you look at?


Typically, I have a standard order of maps and images I will use when I start looking at a property. First, I like to look at the most recent satellite imagery for the property and then relate features to a topographic map. Then I look at the historical aerial photographs for the location, the historical land use, and what could have affected the species currently out there. Then it is also good to look at the soil maps for a property to determine what species might grow on the site. Combining and considering the imagery and maps allows managers to make a more informed decision about what should be on the site and how to achieve it.


Satellite Imagery and Topography

Historic Aerial Photography

Soil Maps


 

Satellite Imagery



Satellite imagery is the most common of the map types that we will look at in the post. Most people have seen a satellite image, whether it be on a GPS, computer, or phone. When selecting a satellite image, it is crucial to choose a recent scan to represent best what is currently out there. Some of the programs I use are OnX maps and Google Earth because they are compatible with both mobile and desktop applications. I appreciate the features of OnX that allow me to sign in to my account on either my phone or computer and see my map features. I use OnX maps primarily for drawing out stands when preparing to conduct a management activity such as clearing brush, creating roads and trails, or implementing a prescribed fire. Google Earth is excellent at scouting a property to determine what type of species is currently out there. It has the most updated images, and since it most often collects images during the winter, you can select the evergreen and deciduous trees more easily.



Topographic maps take images a step further so you can see the slope of your property. The

slope and elevation of your property can dramatically impact what species will be suitable for your site. These maps also help to determine appropriate management activities; for example, a logger is not able to cut trees on a hillside that is too steep. Another example is fire; it behaves very differently, moving up or down a slope or across flat ground. Understanding the topography can be very useful when deciding what species should go on a site and what management activities would be best to achieve this. OnX maps have good functionality with their topographic maps and even have a layer that overlays topographic lines on top of a satellite image. Another good resource for topographic maps is the USGS topographic database which allows you to have topographic maps printed and download georeferenced PDFs that you can add to a program like Avenza maps.


Historic Aerial Photography



Although current satellite images can provide information about what is currently on the site, they often leave out the site's historic use. Historic use can be significant in determining why the species on your property are there. It may seem trivial initially, but looking at historic imagery can tell us when the trees on our property were harvested and whether the land had been farmed. A good resource for historical aerial photos in Alabama is the University of Alabama's Air Photo Archive, which provides images back to the late 1930s.


While historic photos can't tell us everything, and there are periods in between when the photos were taken, it can be beneficial to consider them. It is also neat to look at them from a property owner's perspective. A lake near my property was established in the early 1960s. The early aerial photos from the 1930s and 40s show what the area looked like when it was just the river. That may only tell us a little about the current land; however, it is always beneficial to understand as much about the land as possible.


Soil Maps



Once we have looked at the current satellite images and understand the topography, and the historical use of the land, we can apply those to understanding a soil map. Maps that show the soil classes on a site are crucial to understanding what species should grow there. Often, I hear a site is an upland or a bottomland to describe what habitat should be out there. Topography can help differentiate between habitats; however, we often associate habitat types with soil drainage. Most often, bottomland sites are thought of as holding more water than an upland site which has better drainage. What determines the drainage, though? Soil. Looking at what soil types and soil categories are listed for the site can help managers determine how well the site drains. The Natural Resource Conservation Service's Web Soil Survey is excellent for receiving soil maps. In Web Soil Survey, you can select the area you are interested in, and it shows a map of the different soil types with a description of each and tells the drainage.


Looking at the soil drainage classification of the area helps managers determine whether the site is more suitable for a drier upland species or a wetter bottomland species. Combining that with topographic maps allows managers to more finely pinpoint stand boundaries to combine areas with similar species and management. To determine the species on the site, it can be helpful to look at satellite images and get out on the site and walk around. Understanding the past use of the land determined from historical aerial photographs assists managers in understanding how the land got to where it is and what needs to happen to bring it to their objectives. While it takes some digging, many resources are available to provide landowners and managers with a plethora of maps to assist them in land management.

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