Visual Image Interpretation of Photographs and Images
Image interpretation of remote sensing data is to extract qualitative and quantitative information
from the photograph or imagery.
It involves identification of various objects on the terrain which may be natural or artificial
consists of points, lines, or polygons.
1. Tone:
• In aerial images, tone refers to variations in brightness and color that distinguish different
surface materials. It helps in identifying features such as water bodies (dark tones), sandy
areas (light tones), or urban regions (grey tones).
• Example: In a black-and-white aerial image, a forest may appear as a mid-tone area due
to dense vegetation, while a river will have a darker tone indicating the presence of water.
2. Size:
• The size of objects in aerial photographs provides an understanding of their scale and
importance. Large features such as airports, lakes, or industrial complexes can be easily
identified based on their dimensions.
• Example: In an aerial map, a sports stadium may appear significantly larger than
surrounding residential houses, making it a notable landmark.
3. Shape:
• Shape refers to the geometric outline of objects, which is critical for recognition in aerial
imagery. Different landforms and structures have distinctive shapes.
• Example: Rectangular shapes may indicate crop fields or parking lots, circular shapes
might suggest water reservoirs, and irregular shapes could represent natural features like
forests or wetlands.
4. Texture:
• Texture describes the surface quality of features. It can be coarse, smooth, fine, or
mottled, depending on the pattern or details visible in the image. Texture helps
distinguish between vegetation types, soil conditions, or built environments.
• Example: In a high-resolution aerial image, a forest may show a coarse texture due to the
uneven canopy of trees, while a paved road will have a smooth texture.
5. Pattern:
• Patterns are the arrangements or repetitions of features, which help identify human-made
or natural characteristics. Regular patterns often indicate planned infrastructure, while
irregular ones suggest organic growth.
• Example: A series of evenly spaced parallel lines might indicate agricultural fields with
rows of crops, while a scattered pattern could represent rural housing or natural
vegetation.
6. Shadow:
• Shadows provide clues about the height and orientation of objects in aerial images. By
analyzing shadow lengths, one can infer the dimensions of buildings, trees, or towers.
• Example: Tall buildings in an urban area will cast long shadows that reveal their height,
particularly in low-angle light conditions like early morning or late afternoon.
7. Site:
• Site refers to the location or positioning of features relative to their surroundings.
Understanding site helps contextualize landforms and structures.
• Example: A river might be located near a forested area, suggesting a natural ecosystem,
while a factory situated near a highway might indicate industrial activity.
8. Association:
• Association refers to the relationships between features visible in the image. Certain
objects or structures are often found in proximity to one another, providing context.
• Example: Railways are typically associated with train stations and urban areas, while
large water bodies are often linked with nearby dams or agricultural irrigation systems.
