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Spatial data and Attribute data

Spatial Data

Definition:
Spatial data represents the geometric location of features on the Earth's surface. It defines the shape, size, and position of geographic entities.

Key Concepts and Terminologies:

  • Geometric Representation:

    • Point Data: Represents a single location (e.g., a city center, weather station).
    • Line Data: Represents linear features (e.g., roads, rivers).
    • Polygon Data: Represents area-based features (e.g., administrative boundaries, lakes).
  • Coordinate Systems & Projections:

    • Geographic Coordinate System (GCS): Uses latitude and longitude (e.g., WGS 84).
    • Projected Coordinate System (PCS): Converts curved surface data to a flat map (e.g., UTM, Mercator).
  • Data Formats:

    • Vector Data: Stores discrete features (points, lines, polygons).
    • Raster Data: Stores continuous data in grid format (e.g., satellite imagery, elevation models).

Examples of Spatial Data:

  • A vector dataset of roads with line geometries stored in Shapefile (.shp) format.
  • A raster dataset of land surface temperature stored in GeoTIFF (.tif) format.

2. Attribute Data

Definition:
Attribute data is the descriptive (non-spatial) information attached to each spatial feature. It provides additional characteristics about the location.

Key Concepts and Terminologies:

  • Types of Attribute Data:

    • Nominal Data: Categorical labels (e.g., land cover type: "forest", "urban").
    • Ordinal Data: Ranked values (e.g., soil erosion severity: "low", "medium", "high").
    • Interval Data: Numeric values without a true zero (e.g., temperature in Celsius).
    • Ratio Data: Numeric values with a true zero (e.g., population, rainfall in mm).
  • Attribute Tables:

    • Data is stored in tabular form linked to spatial features.
    • Columns represent attributes (e.g., "Name", "Area"), and rows represent individual features (e.g., each city, road, or land parcel).

Examples of Attribute Data:

  • A city point feature with attributes:

    City NamePopulationElevation (m)GDP ($ billion)
    New York8,398,748101.5
    Tokyo13,515,271402.8
  • A polygon land use dataset with attributes:

    IDLand Use TypeArea (sq km)
    001Residential12.5
    002Commercial5.2

3. Thematic Characteristics

Definition:
Thematic characteristics define the subject or theme of spatial data. They determine what kind of attribute data is associated with each geographic feature.

Key Concepts and Terminologies:

  • Thematic Layers: Different types of spatial information stored separately in GIS.
  • Thematic Mapping: Visualizing data based on specific attributes (e.g., population density maps).
  • Classification Schemes: Grouping data into meaningful categories (e.g., NDVI vegetation classes).

Examples of Thematic Characteristics:

  • Land Cover Theme:
    • Attributes: "Forest", "Grassland", "Urban"
    • Example: A raster dataset showing global land cover classification.
  • Demographics Theme:
    • Attributes: "Population Density", "Age Group Distribution"
    • Example: A choropleth map of population density across districts.
  • Environmental Theme:
    • Attributes: "Temperature", "Precipitation"
    • Example: A raster dataset displaying monthly rainfall distribution.

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