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Geographic DBMS


A Relational Database Model stores data in the form of tables.
Each table contains:

  • Rows → Individual records

  • Columns → Attributes or fields

Tables can be connected using common fields called keys.

Terminologies

1. Table

A collection of related data arranged in rows and columns.

Example:

IDNamePopulation
1Palakkad130000
2Thrissur315000

2. Row (Record)

Represents one feature or entry.

👉 Example
"Palakkad" is one record.

3. Column (Field / Attribute)

Represents one property of data.

👉 Example
Population is a field.

4. Primary Key

A unique field used to identify each record.

👉 Example
ID column.

5. Foreign Key

A field used to connect two tables.

 Example in GIS (QGIS / ArcGIS)

Suppose you have:

Table 1: District Boundary Layer

District_IDDistrict_Name
1Palakkad
2Malappuram

Table 2: Rainfall Data

District_IDRainfall
12200 mm
22800 mm

👉 Both tables share District_ID

Using this field, GIS joins rainfall data to district maps.

Where Used in GIS

  • Attribute tables of shapefiles

  • Linking census data

  • Spatial analysis with external datasets

Geographic DBMS Extensions

A Geographic DBMS Extension adds spatial capability to normal databases.

Normal database → Stores text and numbers
Geographic DBMS → Stores maps, shapes, coordinates

✅ Why It Is Needed

GIS deals with spatial objects like:

  • Points

  • Lines

  • Polygons

  • Raster images

A normal database cannot store or analyse them properly.

✅ Examples of Geographic DBMS Extensions

DatabaseGIS Extension
PostgreSQLPostGIS
OracleOracle Spatial
SQL ServerSpatial Extension

✅ Important Terminologies

1. Geometry

Shape of spatial feature.

Examples:

  • Point → School location

  • Line → Road

  • Polygon → District boundary

2. Spatial Index

Improves speed of spatial queries.

Example:
Finding nearest hospital quickly.

3. Spatial Query

Query based on location.

Example:
"Find all villages within 5 km from river."

✅ Example in QGIS

QGIS uses PostGIS database.

👉 You can store:

  • Road network

  • Land use layers

  • Satellite data

👉 Example Query:
Find all agricultural lands near rivers.

✅ Example in ArcGIS

ArcGIS uses:

  • File Geodatabase

  • Enterprise Geodatabase

They store spatial data with advanced indexing and topology rules.

3. SQL in GIS

✅ Simple Meaning

SQL (Structured Query Language) is used to:

✔ Retrieve data
✔ Filter data
✔ Analyse data
✔ Update data

✅ Basic SQL Commands

1. SELECT → Get data

Example:

SELECT * FROM districts;

👉 Shows all districts.

2. WHERE → Filter data

Example:

SELECT * FROM districts  WHERE Population > 200000;

👉 Shows only high population districts.

3. JOIN → Combine tables

Example:

SELECT districts.Name, rainfall.Amount  FROM districts  JOIN rainfall  ON districts.ID = rainfall.ID;

4. SQL in GIS (Spatial SQL)

GIS uses special spatial functions.

✅ Spatial SQL Terminologies

1. ST_Within

Checks if one feature lies inside another.

Example:
Find houses inside flood zone.

2. ST_Intersects

Checks if two features overlap.

Example:
Find roads crossing rivers.

3. ST_Distance

Finds distance between two objects.

Example:
Distance from school to hospital.

✅ Example in QGIS (Using DB Manager or Expression Builder)

SELECT *  FROM landuse  WHERE ST_Area(geometry) > 10000;

👉 Finds large land parcels.

✅ Example in ArcGIS (Select by Attributes)

"Population" > 100000

✅ Example (Select by Location)

👉 Select villages within 2 km from river.

ArcGIS automatically runs spatial SQL behind the scene.

5. Real Life GIS Workflow Example

Suppose you want to analyse Flood Risk Areas

Step 1 – Store Data

Store rivers, rainfall, and land use in spatial database.

Step 2 – Use Relational Model

Link rainfall table with district boundaries.

Step 3 – Use Geographic DBMS

Store spatial shapes of rivers and villages.

Step 4 – Use SQL

Query villages near river and heavy rainfall zones.

6. Difference Summary

ConceptPurpose
Relational DatabaseOrganizes attribute data
Geographic DBMS ExtensionStores spatial objects
SQL in GISQueries and analyses data

7. Simple Concept Connection

👉 Relational Database
Stores attribute tables.

👉 Geographic DBMS
Stores spatial data.

👉 SQL
Controls and analyses both.

8. Example From Your Field (Geography / GIS Research)

You can use these concepts in:

  • Landslide mapping

  • Urban expansion studies

  • Climate data analysis

  • Crime mapping

  • Poverty mapping


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