Key Points
Key Points: Components of GIS
- GIS has five main components: Hardware, Software, Data, People, and Procedures.
- Hardware includes computers and devices used for data processing, storage, input, display and output.
- Software helps in data entry, editing, analysis, transformation, display and output of spatial information.
- Data (spatial and tabular) is the backbone of GIS; digital maps and databases are essential inputs.
- People and Procedures ensure proper data collection, management, analysis and decision-making using GIS.
Key Points: Spatial Analysis
- GIS is powerful because of its spatial analysis ability, which makes it different from other information systems.
- Spatial analysis uses both spatial (location) and non-spatial (attribute) data to answer real-world questions.
- The main aim of spatial analysis is to convert raw data into useful information for decision-making.
- Before doing analysis, it is necessary to identify the problem and define the purpose clearly.
- Important GIS spatial analysis methods include overlay analysis, buffer analysis, network analysis, and digital terrain model (DTM).
- Overlay analysis combines two or more thematic map layers of the same area to produce a new map, useful for land use change and suitability studies.
- Buffer analysis creates a zone around a point/line/area feature to study nearby affected or benefited areas, such as hospital access or pollution impact.
Key Points: Advantages of GIS over Manual Methods
- Traditional maps have limitations as they show fixed themes and cannot be easily changed without drawing a new map.
- GIS stores data separately (spatial and attribute data), allowing flexible analysis and presentation.
- Users can query spatial features and retrieve related attribute information for better analysis.
- GIS allows creation of new maps by analysing and processing stored data.
- It can perform spatial operations like overlay and buffering, and link different data using shared location codes.
Key Points: Comparison of Raster and Vector Data Formats
| Raster Model | Vector Model |
|---|---|
| Advantages | Advantages |
| Simple structure | Compact structure |
| Easy overlay | Good for network analysis |
| Works with satellite images | Accurate maps |
| Represents high variability well | Efficient projection |
| Disadvantages | Disadvantages |
| Needs more storage | Complex structure |
| Less accurate shapes | Difficult overlay |
| Weak in network analysis | Not suitable for satellite images |
Key Points: Spatial Information Technology (SIT) & GIS
- Spatial means anything related to space and location, like features spread over the Earth’s surface.
- Many modern data have a spatial component, such as addresses, land boundaries, and facility locations.
- Spatial Information Technology is used to collect, store, analyse, manage and display spatial data using technology.
- It is a combination of Remote Sensing, GPS, GIS, Digital Cartography and Database Management Systems.
- GIS (Geographical Information System) is a computer-based system that helps in capturing, storing, checking, analysing and displaying Earth-related spatial data.
- GIS works with two types of data:
i. Spatial data (location, shape, area)
ii. Non-spatial/attribute data (information about the feature) - Spatial data in GIS can be obtained by digital data suppliers, digitising maps, or conducting surveys, and the choice depends on application, budget, and data type (vector/raster).
Key Points: Raster and Vector Data Format
- Raster format is mainly used for aerial photos, satellite images, scanned maps and backdrop maps.
- Raster is useful when cost is low and detailed analysis of individual features is not required.
- Vector format represents features using coordinates (X, Y, Z) and stores points, lines and polygons.
- Vector data is suitable for high accuracy mapping, smaller file size, and analysis of specific map features.
- Vector format can store topology and descriptive information, and manual digitising is the best input method.
Key Points: Sequence of GIS A ce of GIS Ace of GIS Activities ctivities
- Sequence of GIS Activities: GIS work involves spatial data input, entering attribute data, data verification and editing, linking spatial and attribute data, and finally spatial analysis.
- Sources of Spatial Data: Spatial data can be obtained from digital data suppliers or created manually through digitisation and scanning. Data compatibility (scale, projection, quality) must be checked before use.
- Manual Data Input: Manual input includes entering spatial and attribute data, verifying and editing them, and linking both types of data. Methods depend on whether the system uses raster or vector format.
- Digitisation and Scanning: Digitisation converts maps into coordinate-based data, while scanners convert analogue maps into digital raster images for GIS use.
- Data Processing and Cleaning: Scanned images may contain errors or unwanted marks, so extra data must be cleaned and processed before analysis in GIS.
Key Points: Entering the Attribute Data
- Attribute data gives non-spatial information about a feature (e.g., road width, surface type, traffic rules), while the road shape is stored as spatial data.
- Attribute data can be stored separately in relational databases or along with spatial data in object-oriented databases.
- Attribute data can be collected from census reports, surveys, spreadsheets, and published records, and entered manually or imported.
- Data verification and editing is important to remove errors and improve accuracy in GIS data.
- Common digitisation errors include missing data (omissions) and under-shoots or over-shoots in lines.
- Errors may also occur due to wrong scale, distortion of maps, or incorrect geo-referencing, especially in aerial photos and old folded maps.
- Data conversion is needed because all layers must be in the same format (vector or raster); conversion is usually vector to raster for analysis, but raster to vector is used to reduce storage.
Key Points: Geographic Data : Linkages and Matching
- Linking spatial data with attribute data is very important in GIS, because wrong linking can create confusion in analysis.
- GIS helps in combining different data files (e.g., population data and mortality data) to calculate required results.
- Exact matching is done when two files have the same common key (like town name) and records are joined easily.
- Hierarchical matching is used when data is collected at different levels (small areas inside bigger areas) and small data is added to match larger units.
- Fuzzy matching is used when boundaries of two datasets do not match (e.g., soil boundary and crop boundary), so overlay method is used for analysis.
