Texture: Refers to the frequency of tonal changes in an image. Texture is produced by an aggregate of unit features, which may be too small to be clearly discernible individually on the image. It is a product of their individual shape, size, pattern, shadow and tone. By definition, texture is dependent on the scale. As the scale of the photograph is reduced the texture of a given object becomes progressively finer and eventually disappears. Some of the terms often used to describe relative texture values qualitatively are coarse, fine, medium, smooth, rough, etc., it is rather easier to distinguish various textural classes visually than in the digital-oriented techniques.
Pattern:The pattern relates to the spatial arrangement of the objects. The repetition of certain general forms or relationships is characteristic of many objects, both natural and man made, and gives objects a pattern which aids the image interpreter in recognizing them. For example, interbedded sedimentary rocks typically gives an alternating tonal pattern which aids in their identification.
Shape:Relates to the general form, configuration or out line of an individual object. Shape is one of the most important single factor for recognizing objects from images. For example, a railway line is usually readily distinguished from a highway or a kuchha road because its shape consists of long straight tangents and gentle curves as opposed to the shape of a highway. The shape of an object viewed from above may quite different from its profile view. However, the plan view of object is more important and sometimes conclusive indication of their structure, composition and function is possible.
Size:The size of an objects can be important tool for its identification. Objects can be misinterpreted if their sizes are not evaluated properly. Although, the third dimension, i.e., height of the objects, is not readily measurable on satellite images, but valuable information can be derived from the shadows of the objects. Images with stereoscopic coverages, such as those from SPOT and CARTOSAT-1 & 2 provide information on third dimension (height). For planar objects, it is easier to calculate the areal dimensions on imagery, for example-alluvial fan, flood plain, etc.Shadows: are of importance to photo interpreters in two opposing respects (1) The outline or shape of a shadow affords a profile view of objects, which aids interpretation, and (2) objects within shadow reflect little light and are difficult to discern on photographs, which hinders interpretation.Association: It is one of the most helpful clues in identification of land forms. For example, a flood plain is associated with several fluvial features such as terraces, meanders, ox-bow lakes, abandoned channel, etc. Similarly, a sandy plain in a desert is associated with various types of sand dunes.
Terrain ElementsIn addition to the image elements described above, the terrain elements listed below are also very useful for image interpretation. The terrain elements include drainage patterns, drainage dens...