GIS Data Models/Core Functionalities of GIS/Raster to Vector Conversion

GIS Data Models

There are two primary ways to represent the real world within a computer system using GIS:

1. Vector Data

This model uses Points, Lines, and Polygons to represent features.

• Usage: It is most accurate for representing roads, railway lines, electric poles, and property boundaries.

• Characteristics: It occupies less storage space and better explains Topology (the spatial relationship between objects).

2. Raster Data

This model uses Pixels or grid cells.

• Usage: Primarily used for Satellite Imagery and aerial photographs.

• Characteristics: It is better for representing continuous surfaces with fuzzy boundaries, such as soil types or pollution levels.

---

Core Functionalities of GIS

GIS is not just a digital map; it is a powerful analytical tool. Its main functionalities include:

1. Buffering

Creating a fixed-distance zone (radius) around a point, line, or area.

• Example: Identifying flood-affected zones if a pipeline bursts or establishing "no-construction zones" on both sides of a highway.

2. Overlay Analysis

Placing one type of data layer over another to derive new conclusions.

• Example: Overlaying a soil-type layer onto a drainage layer to determine the best site for construction.

3. Network Analysis

Used to understand the flow and routing within a web of pipelines or roads.

• Example: Finding the Shortest Path to minimize traffic congestion or optimize supply chains.

4. Terrain Analysis

Creating 3D models to examine land elevation, slopes, and environmental impacts.

---

Advantages for Civil Engineers

Why is the use of GIS growing?

• Paperless Workflow: No need for bulky physical plans and registers.

• Speed: Updating and editing data is significantly easier and faster.

• Better Decision Making: Testing 'What-if' scenarios (e.g., If a dam is built here, which areas will be submerged?).

• Data Security: Centralized databases ensure that information is never lost.

---

Raster to Vector Conversion (Digitization)

This is the process of converting pixel-based raster images (like scanned maps or satellite photos) into mathematical lines and points (Vectors).

Why is it necessary?

Raster data (like .jpg or .tiff) becomes "pixelated" (blurry) when zoomed in, making precise measurements difficult. In contrast, Vector data maintains its clarity at any zoom level, allowing for accurate calculations of area and length.

The Conversion Process

1. Pre-processing: Improving the quality of the raster image by removing "noise" (unwanted dots) and using Thresholding to make the image binary (Black & White).

2. Vectorization/Tracing:

   • Manual Tracing: The surveyor draws lines over the raster image using a mouse (Heads-up digitizing).

   • Automatic Tracing: Software recognizes pixel patterns and converts them into lines automatically.

3. Post-processing: Refining the converted lines through Line Smoothing and building Topology to ensure all lines connect correctly.

---

Raster vs. Vector: At a Glance

Feature	Raster	Vector
Structure	Pixels / Grid Cells	Points, Lines, Polygons
Storage	Occupies more space	Occupies less space
Zooming	Clarity decreases	Clarity is maintained
Primary Use	Satellite imagery, Photos	Cadastral maps, Engineering drawings

---

NTS Study Pro-Tip: This conversion is the first step in integrating old paper maps into a modern GIS. Without it, you cannot perform advanced analysis like buffering or network routing on legacy data.

Solve the Practice Set below to check your preparation!

🏗️ Surveying: Complete Study Guide & Index

📔 Part 1: Fundamentals of Surveying

• Surveying: A Bird's Eye View – Meaning and significance of land surveying.

• Fundamental Principles – Classification and types of surveying.

• Primary Division – Understanding Plane vs. Geodetic Surveying.

• Representative Fraction (RF) – Utilization of scales and reduction factors.

📏 Part 2: Linear Measurement & Chain Survey

• Chain Surveying – Basic procedures and workflow.

• Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.

• Distance Measurement Methods – Detailed discussion on linear surveying tools.

• Tape Corrections – Adjustments for Sag, Temperature, and Pull.

🧭 Part 3: Angular & Instrumental Survey

• Compass Surveying – Magnetic bearing survey and its applications.

• Plane Table Surveying – Equipment used and graphical methods.

• Theodolite Surveying – Horizontal and vertical angle measurement.

• Total Station – Components, features, and modern digital use.

🏔️ Part 4: Levelling & Elevation

• Need for Levelling – Why vertical measurement is vital in civil engineering.

• Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.

• Operating Levelling Instruments – Handling Auto Level and Tilting Level.

🛰️ Part 5: Modern Technologies

• Remote Sensing – Information on INSAT and IRS Series satellites.

• GIS & LIS Systems – Geographic data management and functionality.

• Laser Scanning – Advanced application and control.

• Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

📝 Part 6: Practice & Quizzes (MCQs)

• Surveying Quiz 1 (01-25) – GPS, Remote Sensing, and Photogrammetry.

• Surveying Quiz 2 (26-50) – Ranging, EDM, and Tacheometry.

• Surveying Quiz 3 (51-75) – Contouring and HI Method Levelling.

• Surveying Quiz 4 (76-100) – Transition Curves and Bowditch Rule.

• Surveying Quiz 5 (101-125) –  Plane table and Compass

• Surveying Quiz 6 (125-150) –  Theodolite Surveying and Levelling

• Surveying Quiz 7 (151-175) –  Tacheometry, Curves, Modern Surveying Instruments (EDM/GPS)

• Surveying Quiz 8 (175-200) –  Area & Volume Calculation, Minor Instruments

---

📚 Quick Revision Resources

• Surveying Top 1-100 One-Liners

• Surveying Advanced (101-200) One-Liners

• Surveying Master Class (Part 1)

• Surveying Master Class (Part 2)

• Quick Revision Guide

• Quick Surveying Formulas

---

Surveying IS Codes with Latest Revision Years

1. General Surveying & Instruments

• IS 1491:1959 – Specification for Prismatic Compass (Liquid and Non-liquid).

• IS 1963:1981 – Specification for Bubbles for Surveying Instruments.

• IS 2988:1995 – Glossary of Terms Relating to Surveying Instruments.

• IS 1634:1992 – Code of Practice for Design and Construction of Storage for Surveying Instruments.

---

2. Chain and Tape Surveying

• IS 1492:1970 – Specification for Metric Surveying Chains.

• IS 1269 (Part 1):1997 – Material and Construction of Steel Tapes.

• IS 1269 (Part 2):1997 – Woven Metallic and Glass Fibre Tapes.

• IS 1659:2006 – Specification for Invar Tapes for High Precision Measurement.

---

3. Theodolite and Tacheometry

• IS 8002:1976 – Specification for Surveying Chain Vertical Vernier Theodolite.

• IS 8330:1976 – Specification for Tilting Levels (Optical).

• IS 8636:1977 – Specification for Tacheometers.

---

4. Leveling and Contouring

• IS 9128:1992 – Specification for Tilting Levels.

• IS 9573:1980 – Specification for Automatic Levels.

• IS 1779:1961 – Specification for 4-metre Leveling Staff (Folding Type).

---

5. Modern Surveying (Total Station & GPS)

• IS 16481:2016 – Guidelines for Accuracy and Testing of Total Stations.

• IS 14855:2000 – Terminology and Concepts for GIS and Remote Sensing.

---

6. Measurement of Building Works

• IS 1200 (Part 27):1992 – Method of Measurement of Building and Civil Engineering Works (Earthwork & Surveying).