📚 GIS Basics – Chapter 3: Spatial Data Acquisition & Preparation
(CTEVT Diploma in Geomatics Engineering – 3rd Semester Notes + Free PDF + Video)
🌍 Before any analysis, mapping, or visualization can be done in GIS, spatial data must be properly collected, prepared, and organized.
Chapter 3 of GIS Basics (3rd Semester) introduces the complete workflow of data acquisition, conversion, cleaning, error correction, and preparation for GIS use.
📥 Download the Full Chapter 3 Notes (Free PDF)
🎥 Watch the Chapter 3 Video on YouTube
🎥 Watch the Full Chapter 3 Video
👉 [Click Here to Watch on YouTube]
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📌 Overview
GIS depends on accurate, reliable, and well-prepared spatial data.
This chapter explains:
- Sources of spatial and non-spatial data
- Data acquisition methods (field survey, remote sensing, GPS, maps)
- Data conversion (analog → digital)
- Geo-referencing
- Digitization
- Data quality, errors, and correction
- Preparing attribute tables
- Data integration for GIS projects
This chapter forms the foundation for all GIS applications.
🗂️ 1️⃣ Types of GIS Data
GIS uses two major data types:
🌍 A. Spatial Data
Represents the location, shape, and geometry of features.
Forms of Spatial Data
- Point (wells, trees, schools)
- Line (roads, rivers, boundaries)
- Polygon (lakes, parcels, land use zones)
Sources
- Survey maps
- Cadastral records
- Remote sensing images
- GPS/GNSS data
- Aerial photographs
📝 B. Attribute Data
Provides descriptive information about spatial objects.
Examples:
- Population of a city
- Road type
- Land use category
- Soil type
- Building height
Stored in tables linked to spatial features.
📸 2️⃣ Spatial Data Acquisition Methods
GIS acquires data from two major groups:
📌 A. Primary Data Sources (Original & Direct)
Collected directly from the field.
✔ Field Survey
Using:
- Total Station
- Theodolite
- Leveling instruments
- GIS survey forms
✔ GPS/GNSS Survey
Used for:
- Mapping boundaries
- Utility pole location
- Road centerlines
- Control points (GCPs)
✔ UAV / Drone Survey
Used for:
- Orthophotos
- Digital Terrain Models (DTM)
- Land use mapping
📌 B. Secondary Data Sources (Existing Data)
Collected from organizations or existing datasets.
Includes:
- Topographic maps
- Cadastral maps
- Satellite images
- Survey Department data
- Forest maps
- DEMs, LULC datasets
- Government reports/statistics
🖥️ 3️⃣ Data Conversion (Analog → Digital)
To use paper maps or scanned charts in GIS, they must be converted to digital form.
Conversion includes:
- Scanning
- Geo-referencing
- Digitization
- Topology building
- Attribute assignment
📌 4️⃣ Geo-referencing
Assigning real-world coordinates to scanned maps or images.
Steps:
- Load raster image
- Identify control points
- Apply coordinate system
- Compute RMS error
- Save rectified image
Used for:
- Old maps
- Aerial photos
- Cadastral sheets
✏️ 5️⃣ Digitization
Digitizing converts analog map features into vector layers.
Types:
- On-screen digitization (QGIS/ArcGIS)
- Table digitization (digitizer board)
Output:
- Point/Line/Polygon layers
- Shapefiles
- Geopackages
Digitization must follow topology rules.
✔️ 6️⃣ Data Preparation
After acquiring data, it must be prepared for analysis.
Data Preparation Includes:
🔹 Editing spatial errors
- Overshoot
- Undershoot
- Gap
- Overlap
- Dangles
🔹 Attribute table preparation
- Create fields
- Add values
- Set data type (integer, float, text)
- Join/relate tables
🔹 Data cleaning
- Remove duplicates
- Fix geometry
- Standardize coordinate system
🔹 Data integration
Combining multiple layers:
-
Road + building + land use + DEM + satellite image
Consistent projection & scale are essential.
🧩 7️⃣ Data Quality & Accuracy
Types of Accuracy
✔ Positional Accuracy
✔ Attribute Accuracy
✔ Logical Consistency
✔ Completeness
✔ Temporal Accuracy
Common Sources of Errors
- Survey mistakes
- Digitization errors
- Wrong projection
- Attribute entry errors
- Old/outdated data
🇳🇵 Nepalese Context
Spatial data in Nepal is acquired from:
✔ Survey Department
- Topographical base maps
- 1:25,000 & 1:50,000 maps
- Geodetic control points
✔ Municipalities
- Building footprints
- Road networks
- Land use zoning
- Urban GIS
✔ Government Agencies
- Land Management (Cadastral)
- Forest & Soil Conservation
- Hydrology & Meteorology
- ICIMOD satellite datasets
🧪 Practical Exercises (As Per Syllabus)
1️⃣ Scan a map and import into QGIS
2️⃣ Geo-reference using control points
3️⃣ Perform polygon, line, and point digitization
4️⃣ Edit spatial errors
5️⃣ Create an attribute table
6️⃣ Combine multiple layers and check alignment
7️⃣ Identify positional & attribute errors
8️⃣ Prepare data for thematic mapping
🧠 Key Takeaways
✔ Primary data = field survey, GPS, drones
✔ Secondary data = maps, satellite images, DEMs
✔ Geo-referencing assigns real-world coordinates
✔ Digitization converts maps to vector layers
✔ Data cleaning removes errors
✔ Data preparation ensures accuracy
✔ Consistent projection is essential for overlay
📝 Short Questions
- What is spatial data acquisition?
- Define primary and secondary data.
- What is geo-referencing?
- What is digitization?
- List two digitization errors.
- What is attribute data?
- Define data quality in GIS.
📚 Long / Analytical Questions
- Describe primary and secondary sources of spatial data.
- Explain the steps of geo-referencing a map.
- Discuss digitization and common errors during digitization.
- Explain data preparation in GIS.
- What are the major accuracy issues in spatial data?
- Describe the importance of data integration in GIS.
📂 Download Free PDF Notes – Chapter 3: Spatial Data Acquisition & Preparation
🔽 [Download Notes – Chapter 3 (PDF)]
(Includes diagrams of data sources, geo-referencing, digitization errors, data quality flowcharts)
🎥 Watch the Full Chapter 3 Video
👉 [Click Here to Watch on YouTube]
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