Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Thoughts on Resolution and Scale

Resolution is, basically, the smallest length in ground units at which the identity or characteristics of something can be resolved by looking at the product. For example, what is the diameter of the smallest object that can be seen in an aerial photograph? Clearly, the answer depends on several factors besides the diameter of the object. It involves the reflectance of the object compared with the surrounding ground, the quality of the vision of the person looking at the photo, and the scale of the photo. An 8 × 10 photo of Arizona might allow only an object the size of Phoenix to be visible. Through enlargement of the same photo, however, it might be possible to increase the resolution so that an object 100 feet across could be identified. If further enlargement—no matter how extensive—does not allow identification of objects with diameters smaller than 100 feet, then the resolution of the photo is said to be 100 feet. Thus, it is obvious that resolution and scale are closely linked—the larger the scale, the greater the resolution—up to a certain limit. Beyond that limit, no further information can be obtained from the product simply by enlarging the scale. In previous exercises you have had the experience, looking at raster images, of watching the information disappear as you zoomed in.

If a specific ground area is to be covered, designers must then weigh the relative factors of size, scale, and resolution to determine the most appropriate method ...