An aerial photo of a parking lot.
Experience is critical when developing your knowledge of analyze aerial photographs. The basics of this skill --- most often called aerial photo interpretation --- can be easily taught, but expert interpreters have learned there is no substitute for experience in interpreting an unusual feature. Probably the most important learning tool is to interpret features on a recent aerial photo of a local area with which you are already familiar or can visit. Then you can easily provide "ground truth" for your interpretation of a given feature by checking it against your ground observations of the same feature.
Instructions
1. Note the topographic or geographic location of the feature you're studying. For instance, spotting an isolated, grassy hill in the landscape in some areas of Wisconsin is likely to be a natural phenomenon caused by the movement of rocks and sediments by Ice Age glaciers. The same type of feature in the flatlands of south Florida, however, is more likely to be a large, decommissioned landfill.
2. Note the shape of the feature you're studying. If it's a piece of virgin, rural land, there should be a notable absence of regular geometric shapes like perfect circles, squares, rectangles or straight lines. Regular geometric shapes indicate the presence of human activities (such as road cuts) or structures. Some shapes are readily recognizable, such as highways and baseball fields. Others, such as sewage treatment plants, may not be so obvious to the uninitiated.
3. Measure the size of the feature. Most aerials are reproduced to a particular scale --- 1 inch equals 200 feet, for instance. At that scale, if you measure a feature that looks like an automobile and it's a bit less than 1/10-inch long on the aerial, it's about the right size (approximately 15-feet long) to be a car. If it is 1/4-inch long on the aerial, it's actually 50 feet long --- way too long to be a car.
4. Note the tone, or relative lightness or darkness of the feature. A body of water, for instance, is normally a darker tone than the adjacent land. It takes some experience, however, to discern the difference between an under- or over-exposed photograph and actual tone.
5. Observe the texture of the feature. According to the University of Colorado, texture is "the impression of 'smoothness' or 'roughness' of image features caused by the frequency of change of tone in photographs. It is produced by a set of features too small to identify individually." This characteristic can help you distinguish smooth grass, concrete and water from rougher features such as a forest canopy.
6. Take note of any discernible patterns in the feature. This characteristic lets you distinguish between the random spatial arrangement of unmanaged forest areas versus the regularly spaced arrangement of planted areas in a tree nursery or orchard.
7. Observe and measure the length of the shadow cast by the feature. Shadows aid interpreters in determining the relative heights of various features. A method for determining the height of an object is detailed in a monograph included in the Resources section.
8. Look at the context of the object --- its setting and associated objects nearby. This can provide insight that can help identify what you're looking at. For instance, a power generating plant is usually sited near a large body of water to provide coolant for the plant, and it's also generally near a large supply of fuel (either a railroad or a port where a constant supply of coal or fuel oil is stored and delivered) --- unless it's nuclear powered.
Tags: aerial photo, body water, feature studying, geometric shapes, long aerial, near large, This characteristic