Skip to main content

GIS: Real World and Representations - Modeling and Maps


Geographic Information Systems (GIS) serve as a bridge between the real world and digital representations of geographic phenomena. These representations allow users to store, analyze, and visualize spatial data for informed decision-making. Two key aspects of GIS in this context are modeling and maps, both of which are used to represent real-world geographic features and phenomena in a structured, analyzable format.

Let's delve into these concepts, terminologies, and examples in detail.

  • 1. Real World and Representations in GIS

    • Concept: The real world comprises physical, tangible phenomena, such as landforms, rivers, cities, and infrastructure, as well as more abstract elements like weather patterns, population densities, and traffic flow. GIS allows us to represent these real-world phenomena digitally, enabling spatial analysis, decision-making, and visualization.

      The representation of the real world in GIS is achieved through various models and maps, which simplify and abstract the complexities of the physical world into digital formats that can be easily analyzed, queried, and visualized.

    • Terminologies:

      • Geospatial Data: Data that is associated with a specific location on Earth, often represented in terms of coordinates (latitude, longitude) or spatial features (e.g., roads, buildings).
      • Representation: The digital model of real-world geographic phenomena in GIS, which can take the form of maps, databases, or spatial models.

    • Example:

      • Real World: A city with streets, parks, rivers, and buildings.
      • Representation: The city's data might be stored in a GIS as point data (for buildings), line data (for roads), and polygon data (for parks and land use areas). These representations allow the GIS to analyze and visualize patterns like traffic congestion, flood risks, or land use planning.

  • 2. Modeling in GIS

    • Concept: Modeling in GIS refers to the process of creating digital representations of geographic phenomena. Models are used to abstract complex real-world features into simplified, structured formats that can be analyzed and manipulated. GIS models are essential for representing both discrete objects (e.g., buildings, roads) and continuous phenomena (e.g., temperature, elevation).

      There are two primary types of models used in GIS:

      1. Vector Models
      2. Raster Models

      These models are fundamental in representing real-world data in a way that facilitates spatial analysis and decision-making.

    • Terminologies:

      • Vector Model: A GIS model that represents geographic features as points, lines, and polygons. It is ideal for representing discrete objects or features with well-defined boundaries, such as roads, buildings, or rivers.
        • Point: A single location in space, represented by a set of coordinates (e.g., a well, a city).
        • Line: A series of connected points representing linear features (e.g., roads, rivers).
        • Polygon: A closed shape that represents area-based features (e.g., parks, land parcels, lakes).
      • Raster Model: A GIS model that represents the world as a grid of cells or pixels, where each cell contains a value representing a specific attribute. It is suitable for representing continuous phenomena, such as elevation, temperature, or vegetation.
        • Pixel: A cell in a raster grid that contains a value (e.g., elevation, temperature, land cover type).
      • Topological Model: A model that represents spatial relationships between geographic features, such as adjacency, connectivity, and containment. Topology is crucial for understanding spatial relationships in GIS, particularly in vector data.

    • Example:

      • Vector Model Example: A city map might be represented using vector data, where:
        • Points represent locations of bus stops or fire stations.
        • Lines represent roads, highways, and rivers.
        • Polygons represent land use areas such as residential zones, parks, or commercial areas.
      • Raster Model Example: A digital elevation model (DEM) is a raster model used to represent elevation data across a landscape. Each pixel in the DEM grid holds a value corresponding to the elevation of that location, which can be used for terrain analysis, such as flood risk assessment or watershed modeling.

  • 3. Maps in GIS

    • Concept: In GIS, maps are visual representations of geographic data that help to communicate information about spatial patterns, relationships, and distributions. Maps in GIS are more dynamic and interactive than traditional static maps, as they can display real-time data, multiple layers of information, and allow for spatial analysis.

      Maps in GIS are often composed of layers of data, each representing a different geographic feature or phenomenon. These layers can be combined to create a comprehensive map that shows various aspects of the real world, such as land use, roads, weather patterns, or population density.

    • Terminologies:

      • Map Layer: A single thematic layer of data in a GIS map. For example, one layer might show roads, while another layer shows water bodies, and another layer shows population density.
      • Thematic Map: A type of map that emphasizes a specific theme or subject, such as population density, land use, vegetation types, or climate zones.
      • Cartographic Representation: The way in which geographic data is visually represented on a map, including aspects like colors, symbols, and scale.

    • Example:

      • Thematic Map: A GIS-based land use map may show areas of a city dedicated to residential, commercial, industrial, and recreational purposes. Different colors may represent different land use types (e.g., blue for water, yellow for residential, green for parks).
      • Topographic Map: A GIS map could represent the elevation of a region using contour lines or a color gradient (e.g., dark green for low elevation and brown for higher elevation). This type of map is useful for analyzing terrain and planning infrastructure.
      • Flood Risk Map: A GIS map could combine layers of land elevation, rainfall data, and river flow to create a flood risk map that highlights areas most likely to be affected by floods. Maps in GIS are interactive, allowing users to zoom, pan, and query data. For example, a user could click on a specific building in a map to get information about its type, height, and surrounding environment.

  • 4. Connecting Modeling and Maps

    The relationship between modeling and maps in GIS is crucial. Maps are visual representations of models, which are digital representations of real-world phenomena. While models abstract and simplify geographic data, maps are the output or visualization of that data, often representing multiple models or layers of information simultaneously.

    • Terminologies:
      • Layering: The process of combining multiple data layers (representing different models or phenomena) to create a composite map. Each layer is typically a different representation of geographic data, such as roads, land use, and elevation.
      • Interactive Maps: Digital maps that allow users to interact with data, zoom in on specific features, or query information about particular geographic elements.
    • Example:
      • Urban Planning Map: A GIS map used for urban planning might combine several layers: one showing road networks (vector data), another showing zoning districts (polygon data), and another showing flood-prone areas (raster data). This composite map would help urban planners make informed decisions about where to build new infrastructure or which areas need flood mitigation measures.

Fyugp note 

GIS second semester 


Comments

Post a Comment

Popular posts from this blog

Platforms in Remote Sensing

In remote sensing, a platform is the physical structure or vehicle that carries a sensor (camera, scanner, radar, etc.) to observe and collect information about the Earth's surface. Platforms are classified mainly by their altitude and mobility : Ground-Based Platforms Definition : Sensors mounted on the Earth's surface or very close to it. Examples : Tripods, towers, ground vehicles, handheld instruments. Applications : Calibration and validation of satellite data Detailed local studies (e.g., soil properties, vegetation health, air quality) Strength : High spatial detail but limited coverage. Airborne Platforms Definition : Sensors carried by aircraft, balloons, or drones (UAVs). Altitude : A few hundred meters to ~20 km. Examples : Airplanes with multispectral scanners UAVs with high-resolution cameras or LiDAR High-altitude balloons (stratospheric platforms) Applications : Local-to-regional mapping ...
Post a Comment
Read more

Types of Remote Sensing

Remote Sensing means collecting information about the Earth's surface without touching it , usually using satellites, aircraft, or drones . There are different types of remote sensing based on the energy source and the wavelength region used. 🛰️ 1. Active Remote Sensing 📘 Concept: In active remote sensing , the sensor sends out its own energy (like a signal or pulse) to the Earth's surface. The sensor then records the reflected or backscattered energy that comes back from the surface. ⚙️ Key Terminology: Transmitter: sends energy (like a radar pulse or laser beam). Receiver: detects the energy that bounces back. Backscatter: energy that is reflected back to the sensor. 📊 Examples of Active Sensors: RADAR (Radio Detection and Ranging): Uses microwave signals to detect surface roughness, soil moisture, or ocean waves. LiDAR (Light Detection and Ranging): Uses laser light (near-infrared) to measure elevation, vegetation...
Post a Comment
Read more

Resolution of Sensors in Remote Sensing

Spatial Resolution 🗺️ Definition : The smallest size of an object on the ground that a sensor can detect. Measured as : The size of a pixel on the ground (in meters). Example : Landsat → 30 m (each pixel = 30 × 30 m on Earth). WorldView-3 → 0.31 m (very detailed, you can see cars). Fact : Higher spatial resolution = finer details, but smaller coverage. Spectral Resolution 🌈 Definition : The ability of a sensor to capture information in different parts (bands) of the electromagnetic spectrum . Measured as : The number and width of spectral bands. Types : Panchromatic (1 broad band, e.g., black & white image). Multispectral (several broad bands, e.g., Landsat with 7–13 bands). Hyperspectral (hundreds of very narrow bands, e.g., AVIRIS). Fact : Higher spectral resolution = better identification of materials (e.g., minerals, vegetation types). Radiometric Resolution 📊 Definition : The ability of a sensor to ...
Post a Comment
Read more

geostationary and sun-synchronous

Orbital characteristics of Remote sensing satellite geostationary and sun-synchronous  Orbits in Remote Sensing Orbit = the path a satellite follows around the Earth. The orbit determines what part of Earth the satellite can see , how often it revisits , and what applications it is good for . Remote sensing satellites mainly use two standard orbits : Geostationary Orbit (GEO) Sun-Synchronous Orbit (SSO)  Geostationary Satellites (GEO) Characteristics Altitude : ~35,786 km above the equator. Period : 24 hours → same as Earth's rotation. Orbit type : Circular, directly above the equator . Appears "stationary" over one fixed point on Earth. Concepts & Terminologies Geosynchronous = orbit period matches Earth's rotation (24h). Geostationary = special type of geosynchronous orbit directly above equator → looks fixed. Continuous coverage : Can monitor the same area all the time. Applications Weather...
Post a Comment
Read more

Man-Made Disasters

  A man-made disaster (also called a technological disaster or anthropogenic disaster ) is a catastrophic event caused directly or indirectly by human actions , rather than natural processes. These disasters arise due to negligence, error, industrial activity, conflict, or misuse of technology , and often result in loss of life, property damage, and environmental degradation . Terminology: Anthropogenic = originating from human activity. Technological hazard = hazard caused by failure or misuse of technology or industry. 🔹 Conceptual Understanding Man-made disasters are part of the Disaster Management Cycle , which includes: Prevention – avoiding unsafe practices. Mitigation – reducing disaster impact (e.g., safety regulations). Preparedness – training and planning. Response – emergency actions after the disaster. Recovery – long-term rebuilding and policy correction. These disasters are predictable and preventable through strong...
Post a Comment
Read more