5. Size

Size of objects in an image is a function of scale of image. It is important to map the size of an object relative to other objects as well as its absolute size (Figure 5.38).

In the context of remote sensing and image analysis, the size of an object is not fixed; rather, it can change depending on the scale of the image being viewed. Scale refers to how much of the real world is represented in the image. For example, a larger-scale image (like a map of a small neighborhood) will show details of objects more clearly, whereas a smaller-scale image (like a map of a continent) may compress those details.

Think of it like viewing a city from an airplane versus standing on the street. From the airplane, buildings look small compared to the overall landscape, whereas from the street, the same buildings appear much larger and more defined. This illustrates how perspective (or scale) affects how we perceive the size of objects.

The size of a feature will change on different scale images. A building may look like a point feature on a small scale image. For example, zones of land use, large buildings such as factories or warehouses would indicate commercial property, whereas small buildings would indicate residential use.

In different scale images, the relative size of objects can shift dramatically. For example, on a small-scale image that covers a large area, a building might appear as a mere point, making it difficult to identify its purpose (commercial vs. residential). In contrast, in a large-scale image focused on a city block, that same building can be more clearly recognized as a factory or a warehouse, helping to delineate land use patterns.

Imagine a toy car and a real car. If you were looking at a toy car from a distance, it might seem insignificant, like just a speck on the road. However, if you approached it and got closer, you would see its details and realize it's a toy car. This is similar to how different scales in images can change the perception of size.

For example, zones of land use, large buildings such as factories or warehouses would indicate commercial property, whereas small buildings would indicate residential use.

The interpretation of size in images can provide insights into land use. Large structures typically suggest commercial activities (like factories), while smaller buildings generally imply residential areas. Therefore, understanding size helps in categorizing different land uses effectively, which is crucial for urban planning, resource management, and environmental monitoring.

Consider a city skyline. When looking at it from a distance, you can identify the large skyscrapers as commercial buildings. As you get closer, you notice smaller homes interspersed. This reflects how images can inform us about urban development and land use based on the size of the structures observed.

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