Skip to main content

Raster Data Model


A raster data model represents geographic space as a grid of cells (called pixels).

Think of it like a chessboard covering the Earth.

  • Each square = cell / pixel

  • Each cell contains a value

  • That value represents information about that location

Example:

  • Elevation = 245 meters

  • Temperature = 32°C

  • Land use = Forest

The grid is arranged in:

  • Rows

  • Columns

This structure is called a matrix.

GRID Model (Cell-Based Matrix Model)

🔹 Concept

The GRID model is the most common raster structure used in GIS for spatial analysis.

It is mainly used for:

  • Continuous data (data that changes gradually)

  • Sometimes discrete/thematic data

🔹 Structure

  • A 2D matrix (rows × columns)

  • Each cell stores one numeric value

    • Integer (whole number)

    • Float (decimal number)

🔹 Key Terminologies

  • Cell Resolution → Size of each pixel (e.g., 30m × 30m)

  • Spatial Resolution → Level of detail

  • DEM (Digital Elevation Model) → Elevation grid

  • Raster Calculator → Tool for mathematical operations

  • Overlay Analysis → Combining multiple raster layers

🔹 Examples

Example 1: Elevation (DEM)

CellValue
A1250 m
A2260 m

Each pixel stores height above sea level.

Example 2: Temperature Map

Each pixel stores:

  • 28.5°C

  • 30.2°C

🔹 Where It Is Used

  • Slope calculation

  • Watershed analysis

  • Rainfall distribution

  • Land suitability analysis

🔹 Advantages

✔ Excellent for mathematical modeling
✔ Ideal for environmental modeling
✔ Easy for spatial analysis

🔹 Disadvantages

✖ Large storage if resolution is high
✖ Less precise for boundary mapping

 IMGRID / IMAGE Model (Imagery Raster)

🔹 Concept

The Image model stores satellite images, aerial photos, scanned images.

It looks like a grid, but:
👉 Each pixel can store multiple values (multi-band).

🔹 Structure

Each pixel contains:

  • One value (grayscale), OR

  • Three values (RGB), OR

  • Multiple spectral bands (Multispectral imagery)

🔹 Key Terminologies

  • Pixel Intensity

  • Spectral Band

  • Multispectral Image

  • RGB (Red, Green, Blue)

  • GeoTIFF

  • World File (.tfw) → Stores georeferencing info

🔹 Example

Example 1: RGB Image

Each pixel stores:

  • Red = 120

  • Green = 90

  • Blue = 60

These combine to produce a color.

Example 2: Sentinel-2 Image

Each pixel stores:

  • Band 2 (Blue)

  • Band 3 (Green)

  • Band 4 (Red)

  • Band 8 (NIR)

Used for:

  • NDVI calculation

  • Vegetation analysis

  • Urban mapping

🔹 Where It Is Used

  • Remote sensing

  • Image classification

  • Change detection

  • Land cover mapping

🔹 Advantages

✔ Good for visualization
✔ Supports multiple bands
✔ Essential for remote sensing

🔹 Disadvantages

✖ Large file size
✖ Requires preprocessing

MAP Model (Scanned Map Raster)

🔹 Concept

The MAP model represents scanned paper maps converted into digital raster form.

Usually:

  • Binary (0 or 1)

  • Black & White

🔹 Structure

  • High resolution scan (300–400 dpi)

  • Pixel values represent:

    • 1 = Feature present

    • 0 = Background

🔹 Key Terminologies

  • Binary Raster

  • Digitization

  • Vectorization

  • Cartographic Raster

  • Georeferencing

🔹 Example

A scanned topographic map:

  • Black lines = roads (1)

  • White background = empty (0)

Used for:

  • Digitizing boundaries

  • Extracting roads

  • Creating vector layers

🔹 Advantages

✔ Useful as background reference
✔ Helps in vectorization

🔹 Disadvantages

✖ Not suitable for analysis
✖ May contain scanning errors


FeatureGRID ModelIMAGE ModelMAP Model
Data TypeNumeric (continuous/discrete)Spectral valuesBinary / Categorical
PurposeSpatial analysisVisualization & Remote sensingBackground / Digitizing
Cell ValueElevation, rainfallRGB / spectral bands1 or 0
ExampleDEMSatellite imageScanned topo sheet

Raster Storage & Compression Methods

Because raster files can be large, special storage techniques are used.

1️⃣ Cell-by-Cell Storage

  • Stores every pixel value separately

  • Simple but large size

Example:
1 1 1 1 0 0 0 1 1

2️⃣ Run-Length Encoding (RLE)

Compresses repeated values.

Instead of:
1 1 1 1 0 0 0 1 1

Store as:
(4,1) (3,0) (2,1)

Saves space when neighboring pixels are similar.

3️⃣ Quadtree Model

Hierarchical division method.

  • Large uniform areas stored as one block

  • Divides only when values change

Example:
A forest area stored as one big block
Urban area divided into smaller blocks

Used in:

  • Large spatial datasets

  • Efficient storage systems


All three models are raster-based (cell structure), but:

  • GRID → Numerical analysis (DEM, rainfall, slope)

  • IMAGE → Remote sensing & spectral analysis

  • MAP → Scanned cartographic reference


Comments

Post a Comment

Popular posts from this blog

Kuhn’s Paradigms

The given content explains Thomas S. Kuhn’s model of scientific development , its application to geography, and criticisms by Karl Popper, Paul Feyerabend, Michel Foucault , and others. 1. Basic Idea Kuhn argued that science does not develop continuously in a straight line . Instead, scientific development occurs through: Preparadigm → Paradigm → Normal Science → Crisis → Scientific Revolution → New Paradigm A new paradigm may replace an older one, producing a major change in the way scientists understand and study a subject. Concepts and Terminologies Concept / Term Simple Meaning Paradigm A commonly accepted framework/model that guides scientific research Exemplar A successful concrete problem-solution used as a model for future research Disciplinary Matrix Shared beliefs, values, concepts, methods and techniques of a scientific community Preparadig...
Post a Comment
Read more

Regional Geography, Systematic Geography, Idiographic, Nomothetic, Inductive and Deductive Approaches

T wo major ways of studying Geography : the Regional Approach and the Systematic Approach . It also explains the related ideas of idiographic vs. nomothetic and inductive vs. deductive reasoning , especially in the context of the Hartshorne–Schaefer debate . 1. Regional Geography: “All About One” Regional Geography studies one particular region in detail . A region is an area that has some degree of homogeneity (sameness) within its boundary but is also unique or different from other regions . For example, if we study Palakkad District , we may study: Relief and drainage Climate Soil Vegetation Agriculture Population Occupation Economy Culture Political characteristics The purpose is to understand the complete geographical personality of Palakkad and the relationships among its different features. Key concepts Region: A geographical area with identifiable characteristics and boundaries. Homogeneity: Si...
Post a Comment
Read more

Models and Theories in Geography

Geographical Models A model is a simplified representation of reality used to describe, explain, simulate, and predict geographical phenomena. Types Physical (Iconic) Models – Three-dimensional representations (e.g., globe, relief model). Conceptual Models – Diagrams or frameworks explaining geographical relationships. Mathematical (Quantitative) Models – Equations and statistical models for spatial analysis and prediction. Simulation Models – Computer-based models that simulate geographical processes (e.g., climate, flood, urban growth). Major Geographical Models Model Scholar Year Concept Johann Heinrich von Thünen Agricultural Land Use Model 1826 Land use varies with distance from the market. Walter Christaller Central Place Model 1933 Distribution of settlements and services. Ernest Burgess Concentric Zone M...
Post a Comment
Read more

Multispectral and Hyperspectral Imaging Systems

The main idea is how a remote-sensing sensor collects information about an area . A sensor does not simply take an ordinary photograph. It measures the electromagnetic energy reflected or emitted by objects in different wavelength bands . Depending on how many bands are measured and how the sensor collects them, different imaging systems are used. 1. Multispectral vs. Hyperspectral Multispectral imaging (MSI) records information in a limited number of relatively broad, separate spectral bands , such as blue, green, red, near-infrared and shortwave infrared. Hyperspectral imaging (HSI) records information in many narrow and usually contiguous spectral bands . Therefore, it provides a much more detailed spectral signature of each pixel. The resulting dataset is commonly called a hyperspectral data cube (hypercube) because it contains: X-axis → spatial information Y-axis → spatial information Z-axis → wavelength/spectral information Thus, hype...
Post a Comment
Read more

Kuhn’s model in Geography

Thomas Kuhn (1922–1996) Thomas Samuel Kuhn was an American philosopher and historian of science . In 1962 , he published The Structure of Scientific Revolutions , introducing the concepts of paradigm and paradigm shift , which transformed the understanding of scientific progress. Definition: A framework of assumptions, concepts, and values that guide a group or field. Example (Science): Moving from a-earth-centered universe to a sun-centered solar system is a change in the scientific paradigm. Example (Daily Life): A shared cultural belief or a standard way of doing business.   Kuhn's Model (1962) Kuhn's Model explains that science develops through successive paradigms rather than by continuous, gradual progress. Stages of Kuhn's Model Pre-paradigm Stage – No common theory; different ideas exist. Normal Science – Scientists work within an accepted paradigm . Crisis – Anom...
Post a Comment
Read more