GIS Database – Geography – UGC NET – Notes

Geodatabase

• A geodatabase is a database specifically designed to store, manage, and analyze data that is referenced to locations on the Earth’s surface. Unlike conventional databases, a geodatabase integrates spatial data (location and shape) with attribute data (descriptive information).
• Attribute data refers to additional information associated with spatial features. For example, a road feature may have attributes such as name, length, surface type, and traffic volume. Together, spatial data and attribute data allow users to perform advanced geographic analysis, visualization, and decision-making.

Attribute Data

• Attribute data is non-spatial information that describes the characteristics of geographic features. It is stored in tables and linked to spatial features through a unique identifier.

Examples of Attribute Data:

• City: Name, population, state
• Hospital: Name, type, capacity
• Wells: Village name, depth
• Highway: Type, route number
• River: Name, length

Multiple attributes can be attached to a single spatial feature depending on user requirements and application needs.

Spatial Data Formats in GIS

Spatial data in GIS is primarily stored in two formats:

1. Vector Data

2. Raster Data

Each format has its own structure, advantages, and use cases.

Vector Data Formats

• Vector data represents geographic features using coordinates, rather than grids of pixels. It is composed of vertices and paths, making it ideal for representing discrete objects with clear boundaries.
• Simple geometric objects of point, line and polygon and their 𝑥, 𝑦 coordinates are used to represent spatial features. All the features have different dimensions and property, which can distinguish in the below three types.
• Point has 0 dimension and has only the property of location.

Point may also be called:

• Node
• Vertex
• 0-Cell

Line is 1 dimensional and also has property of length. Begins and ends with a node.

Line are also known as

• An edge
• Link
• Chain
• 1-Cell

Polygon is 2 dimensional and has properties of area and perimeter.

Terminologies

Polygons are referred as

• Area
• Region
• Zone
• 2-Cell

Point& Line Features:

• Basic unit of the vector data model are points and their coordinates. Line features are made of points. Between two end points a line is a series of points marking the form of the line.
• Different segments may be created to smooth curve or straight lines. Line features may intersect or join with many other lines and together form network.

Polygon Features:

• Polygons are defined by lines and boundary of an polygon separates the interior area from the exterior area (which may be unbounded). All the area features may be isolated or connected with each other.
• It may form holes within other areas. Area features may overlap and create overlapped areas.

Basic Vector Geometry Types

The entire Earth’s surface—both natural and man-made features—can be represented using three basic vector entities:

• Point: Represents a single location (no area or length)
• Line: Represents linear features with length but no area
• Polygon: Represents enclosed areas with defined boundaries

Examples of Vector Features:

• Point: Hospitals, wells, schools

• Line: Roads, rivers, canals

• Polygon: Forests, agricultural land, urban areas

The Vector Data Model follows an object-based approach and is best suited for representing discrete features such as buildings, roads, and administrative boundaries.