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Model GIS object attribute entity

These concepts explain different ways of organizing, storing, and representing geographic information in a Geographic Information System (GIS). They include database design models (ER model), data structure models (Object and Attribute models), and spatio-temporal representations that integrate location, entities, and time. Together, they help GIS manage both spatial data (where things are) and descriptive information (what they are and how they change over time).

1. Object-Based Model (Object-Oriented Data Model)

The Object-Based Model treats geographic features as independent objects that combine spatial geometry and descriptive attributes within a single structure.

Core Concept:
Each geographic feature (such as a building, road, or river) is represented as a self-contained object that stores both:

  • Geometry – location and shape (point, line, polygon)

  • Attributes – descriptive properties (name, type, length, capacity)

Unlike older georelational models, which stored spatial data and attributes separately, object-based models integrate both into one system.

Key Characteristics

  • Encapsulation: Geometry and attributes are stored together in one object.
    Example: A "Fire Hydrant" object contains its coordinates along with properties like water pressure and color.

  • Behavior (Methods): Objects can perform automatic operations.
    Example: A "Parcel" object can automatically calculate its area when its boundary changes.

  • Inheritance: Objects can be organized in hierarchical classes.
    Example:

    • Parent class: Road

    • Child classes: Highway, Street, Footpath
      These inherit common properties but may also have specialized attributes.

This model is widely used in modern GIS and spatial databases such as object-relational GIS systems.

2. Attribute Model

The Attribute Model explains how non-spatial descriptive information about geographic features is stored and managed.

In GIS, spatial data answers "Where is the feature?", while attribute data answers "What is the feature?".

Structure

Attributes are stored in tables consisting of rows and columns:

  • Rows (Records): Represent individual geographic features

  • Columns (Fields): Represent characteristics of those features

Example

Lake_IDNameDepth (m)Salinity
101Lake A25Low
102Lake B40Medium

Relational Database Approach

Most GIS systems use the Relational Database Model, where tables are connected using a unique identifier (Primary Key).

Example:

  • Spatial layer: Cities

  • Attribute table: Population statistics

  • Linked by City_ID

Data Types

Attributes are stored using appropriate data formats such as:

  • Integer: population, number of houses

  • Float: rainfall, temperature

  • Text/String: place names

  • Date: time of observation

Thus, the attribute model provides structured storage and efficient querying of descriptive geographic data.

3. Entity–Relationship (ER) Model

The Entity–Relationship (ER) Model is a conceptual database design tool used before building a GIS database. It helps represent real-world geographic systems in a structured form.

An ER model is usually shown as a diagram consisting of three components.

Entities
Entities represent real-world objects or phenomena.

Examples:
Forest, River, Village, Ranger Station

Attributes
Attributes describe the characteristics of entities.

Example:
Forest → tree species, area, density

Relationships
Relationships define how entities are connected.

Example:
A River flows into a Lake

Purpose of the ER Model

  • Reduces data redundancy

  • Improves database organization

  • Supports complex spatial queries

Example query:
"Which Ranger Station manages a particular Forest Area?"

Thus, the ER model acts as a blueprint for designing efficient GIS databases.

Spatio-Temporal Representations in GIS

(Location–Entity–Time Triad)

Traditional GIS mainly represents static spatial information (a snapshot of space). However, many geographic phenomena change over time.

To address this, Donna Peuquet proposed the Spatio-Temporal Triad, which organizes geographic data using three perspectives:

  • Location

  • Entity

  • Time

These perspectives help answer where, what, and when questions in GIS.

4. Location-Based Representation

The Location-Based Representation organizes information according to fixed geographic positions.

Key Question:
"What information exists at this location over time?"

Structure

  • Often implemented using raster (grid) data models

  • Each cell represents a fixed location

  • The attribute value of that cell changes through time

Example

Monitoring soil moisture at coordinate (X,Y):

TimeSoil Moisture
Day 130%
Day 235%
Day 340%

Applications

  • Climate monitoring

  • Pollution distribution

  • Land cover change detection

  • Temperature mapping

This model is ideal for studying continuous spatial phenomena.

5. Entity-Based Representation

The Entity-Based Representation organizes data according to specific geographic features or objects.

Key Question:
"Where was this object at different times?"

Structure

  • Usually uses vector data models

  • Each entity has a unique ID

  • The system records how its location, shape, or attributes change over time

Example

Tracking Wildlife Migration

TimeLocation
Day 1Point A
Day 2Point B
Day 3Point C

Applications

  • Vehicle or fleet tracking

  • Wildlife movement studies

  • Hurricane path tracking

  • Urban boundary expansion

This model is best for discrete objects that move or change shape over time.

6. Time-Based Representation

The Time-Based Representation organizes geographic information according to temporal events or time sequences.

Key Question:
"What happened at this particular time?"

Structure

  • Data is arranged along a timeline

  • Each time point stores all spatial changes occurring at that moment

Example timeline:

YearEvent
2000New road constructed
2005Urban expansion
2010Flood event

Applications

  • Disaster analysis

  • Urban development history

  • Environmental change studies

  • Infrastructure development tracking

This representation is useful for event reconstruction and historical analysis.

In summary, these GIS concepts represent different ways of managing geographic data:

  • Object Model – integrates geometry, attributes, and behavior in spatial objects

  • Attribute Model – organizes descriptive data in relational tables

  • ER Model – designs database structure conceptually

  • Location Representation – studies changes at a fixed place

  • Entity Representation – tracks changes of a specific object

  • Time Representation – records events in chronological order

Together, they provide a comprehensive framework for representing spatial and temporal dynamics in modern GIS systems.


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