Air Photo Interpretation Principles

Shape

Size

Shadow

Tone/Color

Texture

Pattern

Relationship to Surrounding Objects

• Because the BLM document is mostly “cartoon” descriptions of images on a photo, we will explore some real examples, using the BLM text to guide our discussions. The photo on the right is a black and white photo of the City of Ithaca and the Cornell University campus taken in 1991. More specifically, it was taken on April 4, 1991 (look in the upper left hand corner).

• So lets take a quick tour of the photograph

• Size: the size of an object is one of the most useful clues to its identity. Also, understanding the size of one object may help us understand the sizes of other objects.

• For example, most of us have a feeling for the size of a baseball field, and football field. When we observe these objects on a photograph, it will help us to understand the sizes of other objects on the photograph.

• For example, on another part of the photograph we have a trailer park. This could easily be confused with a parking lot, but when we understand the size of the objects we will realize that the objects in the trailer park are much too large to be cars.

• Shape: Shapes can often give away an object’s identity. For example, a cloverleaf is a very distinctive feature of a highway, while a stream’s meandering gives away its identity.

• And again, the baseball diamond we just looked at also has a distinctive shape.

• Shadow: shadows often give us an indication of the size and shape of an object. When we look at aerial photographs we often see a vantage point we are not used to: an overhead view.

• Shadows can let us “cheat” alittle to see the side of an object. The photos on the right show the Cornell Theory Center, which casts a rather large shadow, indicating the building size, and a water tower on one of the farms on campus. If you look closely, you can see the “legs” of the watertower.

• Shadow: while shadows are helpful, they can also be a hindrance. As we try to look down into the gorge on the Cornell campus, we can see very little due to the shadows cast.

• Tone: You can see the tonal contrast between Cayuga Lake and the land area. Also, there is good tone representation for wet or dry soils.

• Texture: In this photo we see the Cornell Plantations and Botanical Garden, as well as the experimental agricultural plots. Especially in the Plantations, you will see the different textural characteristics between the mowed lawns and the grassy areas. Notice too, the small pond in the Plantations (an example of tone)

• Additionally, around another natural area on campus you can see the textural difference of trees vs. more of a grassland area.

• And again, as you look at the agricultural plots you will notice a different texture from the forested areas.

• Finally, in the golf course shown below there are obvious patterns between managed lawns vs. the unmanaged lawns, in addition to the tonal differences between the lawns and sand traps.

• Pattern: There are so many examples related to pattern. These would include the rectilinear pattern of the older, urban neighborhoods in Ithaca, the straight lines of trees in an orchard, the rectilinear shape of the experimental agricultural plots, and the configuration of a parking lot.

• Also, the pattern of the golf course with greens, tees, traps, and fairways is very easy to spot.

• Pattern: the drainage pattern for a particular property on this photo is easy to see. Also, because the drainage is relatively straight, we can assume that a moderate to steep slope exists, as water did not have much opportunity to meander.

• Relationship: observing relationships on photographs is one of the most fun observations. For example, a school and a plaza are interpreted differently due to relationships:– While both have many large structures

on them, schools typically have playing fields

– Also, plazas usually have larger parking areas

• Here we see the East Hill Shopping Plaza (no athletic fields, but a campus of buildings), and the Ithaca High School campus (with athletic fields)

• Relationship: here is another example of relationship that shows a middle school and an elementary school. Notice that it have buildings like the high school, and a parking lot, but no real athletic fields to speak of. What it does have, however, is what appears to be a playground, and is surrounded by a residential community.

• The structures on the top are an apartment complex. They could be tractor trailers, but “size” gives them away. They are too large to be tractor trailers when you consider the size of the schools below.

• Notice that just north of the apartment complex is a large pool. How do we know it’s a pool, well, the tone gives us a clue…

Apartments

School

School

• Putting it together: there was a Broadway musical about George Seurat, the French painter who painted with dots. One of the hit songs was called “Putting it Together”, and a line was “bit by bit, putting it together”. In many ways, photo interpretation is putting together our observations bit by bit to form a coherent understanding of the image. For instance, identifying the water treatment plant forces us to use shape, pattern, tone, and relationship to make the connection:

– We see the water holding areas in black (tone)– We see the large tanks (shape)– And when you’ve seen one treatment plant,

you’ve seen them all (pattern)!!

• Notice that across the water is a park. Why do we know it’s a park? Well, again, we see multiple ball fields, not enough buildings to be a school, and a very large pool.