This topic will cover the basics of Geographic Information Systems (GIS), including the concept of spatial data, types of GIS software, and the applications of GIS in various fields.
Introduction to GIS – Quick‑Reference Notes
1. What is GIS?
- Definition: Geographic Information System (GIS) is a computer‑based tool that captures, stores, manages, analyzes, and visualizes spatial (location‑based) data.
- Core Idea: Combines “where” (geography) with “what” (attributes) to reveal patterns, relationships, and trends.
2. Key Components of a GIS
| Component |
Function |
Typical Example |
| Hardware |
Processing power, storage, GPS receivers, plotters, mobile devices |
Desktop workstation, field tablet |
| Software |
GIS platforms & extensions for data handling, analysis, mapping |
ArcGIS, QGIS, GRASS, MapInfo |
| Data |
Spatial (geometry) + attribute (descriptive) information |
Shapefiles, raster images, databases |
| People |
Users, analysts, developers, decision‑makers |
Cartographers, planners, researchers |
| Methods/Procedures |
Standardized workflows for data acquisition, editing, analysis, and sharing |
QA/QC protocols, metadata standards |
3. Types of Spatial Data
| Data Type |
Geometry |
Typical Sources |
Common Uses |
| Vector |
Points, lines, polygons |
GPS surveys, digitized maps, CAD files |
Network analysis, parcel mapping |
| Raster |
Grid of cells (pixels) |
Satellite imagery, aerial photos, DEMs |
Surface modeling, land‑cover classification |
| Tabular (Non‑spatial) |
Linked via IDs |
Census tables, sensor logs |
Attribute joins, statistical analysis |
4. GIS Data Model Basics
- Feature Class – collection of similar geometry (e.g., all roads as polylines).
- Layer – visual representation of a feature class with symbology, labeling, and scale settings.
- Geodatabase – organized storage (file, personal, enterprise) that maintains topology, relationships, and versioning.
- Coordinate Systems
- Geographic (lat/long) – based on a spheroid/ellipsoid.
- Projected – planar, e.g., UTM, State Plane; preserves distance, area, or shape depending on projection.
5. Fundamental GIS Operations
| Operation |
Description |
Example |
| Data Capture |
Collecting raw spatial information |
GPS field survey, digitizing paper maps |
| Georeferencing |
Aligning raster images to real‑world coordinates |
Registering a scanned aerial photo |
| Editing |
Adding, deleting, or modifying features |
Updating road network after construction |
| Query & Selection |
Retrieve features based on attribute or spatial criteria |
Find all schools within 1 km of a river |
| Overlay |
Combine two or more layers to derive new information |
Intersect flood zones with residential parcels |
| Buffering |
Create zones at a set distance around features |
500‑m buffer around highways for noise analysis |
| Spatial Join |
Transfer attributes from one layer to another based on location |
Assign census block population to park polygons |
| Surface Analysis |
Derive terrain attributes (slope, aspect, viewshed) from DEMs |
Identify suitable sites for solar panels |
| Network Analysis |
Solve routing, service area, and flow problems |
Optimize garbage‑truck routes |
| Geostatistics |
Interpolate point data to continuous surfaces |
Kriging of soil moisture measurements |
6. GIS Workflow – Typical Project Cycle
- **Define Problem