Exam-useful questions from this chapter, grouped by marks, each with a full model answer. Try writing the answer yourself first, then check it against this one.
1 1-Mark Questions
Q. Define Spatial Information Technology in one line.
Answer: Spatial Information Technology is the use of technological inputs in collecting, storing, retrieving, displaying, manipulating, managing and analysing spatial information.
Q. What does DBMS stand for?
Answer: DBMS stands for Database Management System.
Q. What does CCD stand for?
Answer: CCD stands for Charged Coupled Devices, the semiconductor sensors used in scanners.
Q. Name the two most common ways of inputting spatial data manually into a GIS.
Answer: Digitisation and Scanning.
Q. Name the three types of matching used in linking spatial and attribute data.
Answer: Exact Matching, Hierarchical Matching and Fuzzy Matching.
Q. Name the four spatial analysis operations mentioned in the chapter.
Answer: Overlay analysis, Buffer analysis, Network analysis and Digital Terrain Model.
Q. What does ‘resolution’ mean in the raster data format?
Answer: Resolution is the relationship between the cell size and the number of cells that make up the raster grid.
Q. Since when have advance computing systems enabled GIS-based processing, per the chapter?
Answer: Since the mid-1970’s.
2 2-Mark Questions
Q. Differentiate spatial and non-spatial data, using the chapter’s Box 4.1 example.
Answer: Spatial data are characterised by their positional, linear and areal forms of appearance and have a definite location on a map, e.g. the literate population of different states (1981), since each state has a definite location. Non-spatial (attribute) data can be located anywhere and are not tied to a map position, e.g. the stock register of a cycle shop, which lists parts and quantities with no map location.
Q. What are the three factors governing the choice of a geographical data source for a GIS application?
Answer: The choice is governed by (i) the application area itself, (ii) the available budget, and (iii) the type of data structure required, i.e. vector or raster.
Q. List the five components of GIS.
Answer: The five components of GIS are Hardware, Software, Data, People and Procedures.
Q. What is Exact Matching? Give the chapter’s own example.
Answer: Exact Matching means bringing together information from two computer files about the same set of geographic features using a key common to both files. The chapter’s example is matching two files about the same towns using the name of the towns as the common key.
Q. What is Hierarchical Matching? Give the chapter’s own example.
Answer: Hierarchical Matching is used when some information is collected in more detail and less frequently than other information. The chapter’s example: land use data covering a large area are collected quite frequently, while land transformation data are collected for small areas but at less frequent intervals. If the smaller areas fit within the larger ones, the data for the small areas are added together until the grouped areas match the bigger ones, and then the two are matched exactly.
Q. What is Fuzzy Matching? Give the chapter’s own example.
Answer: Fuzzy Matching is used when the boundaries of smaller areas do not match the boundaries of larger ones. The chapter’s example is crop-field boundaries, defined by field edges, which rarely match soil-type boundaries; the two are overlaid to compute, for instance, crop productivity for each soil type.
Q. What are the three limitations of maps compared to a GIS?
Answer: (i) Map information is processed and presented in one particular way. (ii) A map shows one or more predetermined themes only. (iii) Altering the information depicted on a map requires an entirely new map to be drawn.
Q. Name the three basic types of error found during data verification, per the chapter.
Answer: (i) Spatial data that are incomplete or double (gaps left by raster-vector conversion). (ii) Spatial data captured at the wrong scale. (iii) Spatial data that are distorted, for example by lens distortion on aerial photographs or by rain, sunshine and folding damage on paper maps.
Q. What is meant by ‘weeding’ algorithms in GIS data editing?
Answer: Where excess coordinates define a line, they may be removed using ‘weeding’ algorithms, one of the editing functions used to correct errors in a vector database.
Q. Which method does the chapter call the best way of vector data input, and what does a vector data model store?
Answer: The chapter states that manual digitising is the best way of vector data input. A vector data model uses points stored by their real (earth) coordinates; lines and areas are built from sequences of points in order, lines have a direction, polygons can be built from points or lines, and vectors can store information about topology.
3 4-Mark Questions
Q. Explain the advantages of GIS over manual methods.
Answer: The chapter lists four advantages: (i) users can interrogate displayed spatial features and retrieve the associated attribute information for analysis; (ii) maps can be drawn by querying or analysing attribute data rather than being redrawn from scratch; (iii) spatial operations such as polygon overlay or buffering can be applied to an integrated database to generate new sets of information; and (iv) different items of attribute data can be associated with one another through a shared location code, letting otherwise separate data sets be combined and analysed together.
Q. Describe the sequence of five activities involved in GIS-related work.
Answer: The chapter names five sequential activities: (i) spatial data input, bringing map geometry into the GIS; (ii) entering the attribute data, the non-spatial properties of each feature; (iii) data verification and editing, checking and correcting both spatial and attribute data for errors; (iv) spatial and attribute data linkages, joining the two data types to the same features; and finally (v) spatial analysis, using the linked, verified database to answer real questions and support decisions.
Q. Explain Overlay Analysis with the chapter’s Aligarh City case study and the Fig. 4.7 formula.
Answer: Overlay analysis integrates multiple thematic map layers of the same area to obtain a new map layer, similar to sieve mapping, i.e. overlaying tracings of maps on a light table to compare them. Fig. 4.7 illustrates this with the formula x + y = z, where x is a road map, y is a rail map, ‘+’ is the spatial overlay operation of union, and z is the resulting transportation map. The chapter’s own worked example is Aligarh City: urban land use maps of 1974 and 2001 were overlaid to detect land-use change and, from that, to map the city’s urban sprawl over the period.
Q. Explain Buffer Operation with the chapter’s western Uttar Pradesh hospital case study.
Answer: A buffer is a zone of a specified distance created around a point, line or area feature; this is called proximity analysis, and it generates polygon feature types. It is used to find how much area or population is served or denied by a facility, such as a hospital. In the chapter’s case study, buffers of 2, 4, 6, 8 and 10 km were created around six cities of western Uttar Pradesh with major hospitals, namely Saharanpur, Muzaffarnagar, Meerut, Ghaziabad, Gautam Budh Nagar and Aligarh. The analysis showed that areas closer to these cities are better served by medical facilities, while people living farther away have to travel longer distances and are the least benefitted.
Q. Compare the raster and vector data formats using Box 4.2.
Answer: Raster’s advantages: a simple data structure; easy and efficient overlaying; compatible with satellite imagery; high spatial variability efficiently represented; simple for one’s own programming; the same grid cells can hold several attributes. Its disadvantages: inefficient use of computer storage; errors in perimeter and shape; difficult network analysis; inefficient projection transformations; loss of information and less accuracy when using large cells. Vector’s advantages: a compact data structure; efficient for network analysis; efficient projection transformation; accurate map output. Its disadvantages: a complex data structure; difficult overlay operations; high spatial variability is inefficiently represented; not compatible with satellite imagery.
Q. Explain the two categories of spatial data input with their sub-stages.
Answer: (a) Acquiring digital data sets from a data supplier: ready-made digital data are used directly, saving the overhead of digitising, but the user must check compatibility factors: scale, geo-referencing system, collection technique/sampling strategy, data quality, classification/interpolation method, size and shape of mapping units, and record length, before combining data from different suppliers; DAT tapes, CD ROMS and floppy disks are named as common transfer media. (b) Creating digital data sets by manual input, which has four stages: entering the spatial data, entering the attribute data, verifying and editing both, and, where necessary, linking the spatial data to the attribute data. This is most commonly carried out by digitisation or scanning.
4 6-Mark Questions
Q. Discuss the meaning of GIS, its formal definition, and the five components of GIS in detail.
Answer: A Geographic Information System (GIS) is the system, made possible by advance computing systems available since the mid-1970’s, that processes georeferenced information to organise spatial and attribute data, integrate them, locate specific information across files, and perform computations and analysis to build a decision support system. The chapter’s formal definition: ‘A system for capturing, storing, checking, integrating, manipulating, analysing and displaying data, which are spatially referenced to the Earth.’ It is an amalgamation of Computer Assisted Cartography and a Database Management System, and it draws its conceptual and methodological strength from twelve allied fields: Computer Science, Statistics, Cartography, Remote Sensing, Database Technology, Geography, Geology, Hydrology, Agriculture, Resource Management, Environmental Science and Public Administration. GIS has five components. Hardware comprises the processing, storage, display and input-output sub-systems. Software supplies the modules for data entry, editing and maintenance; for analysis, transformation and manipulation; and for data display and output. Data, both spatial and tabular, form the backbone of GIS and may be acquired from a supplier or created/collected in-house. People range from hardware and software engineers to resource and environmental scientists, policy-makers, and the monitoring and implementing agencies that use GIS to build a decision support system. Procedures cover how the data are retrieved, input, stored, managed, transformed, analysed and finally presented as output.
Q. Give a detailed account of the raster and vector data formats, their comparative advantages/disadvantages, and where each is best used.
Answer: Raster data represent a graphic feature as a pattern of grids of squares (cells or pixels); each cell is assigned a position in the data file and given a value based on the attribute at that position, and its row/column coordinates identify any individual pixel. The relationship between cell size and the number of cells is called resolution. Raster is best used for digital representations of aerial photographs, satellite images and scanned maps; when costs must be kept down; when individual-feature analysis is not required; and for ‘backdrop’ maps. Vector data instead record the position of a feature by the coordinates of its start and end points (as 2D X,Y or 3D X,Y,Z values); lines have a direction, polygons are built from points or lines, and vectors can store topology, with manual digitising being the best input method. Vector is best used for highly precise applications; when file size matters; when individual map features require analysis; and when descriptive information must be stored. Per Box 4.2, raster’s advantages are a simple data structure, easy overlaying, compatibility with satellite imagery, efficient representation of high spatial variability, ease of own programming, and shared grid cells for several attributes; its disadvantages are inefficient storage use, errors in perimeter/shape, difficult network analysis, inefficient projection transformation, and loss of information/accuracy with large cells. Vector’s advantages are a compact data structure, efficient network analysis, efficient projection transformation, and accurate map output; its disadvantages are a complex data structure, difficult overlay operations, inefficient representation of high spatial variability, and incompatibility with satellite imagery.
Q. Write an explanatory account of the sequence of activities involved in GIS-related work.
Answer: GIS-related work follows five activities in sequence. First, spatial data input: the spatial database is created either by acquiring digital data sets from a data supplier, after checking compatibility of scale, geo-referencing, collection technique, quality, classification method, mapping-unit size/shape and record length, or by manual input, using digitisation or scanning; scanners convert analogue maps into digital grid-based images using CCD sensors, though a scanned image is never perfect and needs its excess data cleaned. Second, entering the attribute data: non-spatial properties, such as a road’s width, surface type, traffic estimate and traffic regulation, are attached to the spatial object in a relational or object-oriented database, drawn from published records, official censuses, primary surveys or spreadsheets. Third, data verification and editing: the captured data are checked for three kinds of error: incomplete or double data, data at the wrong scale, and distorted data, typically by comparing a computer plot on a translucent sheet against the original on a light table, then correcting errors with editing tools such as the keyboard, mouse-controlled cursor or digitiser tablet, using ‘weeding’ algorithms to remove excess line coordinates. Fourth, spatial and attribute data linkages: the two data types are joined, using exact matching (a common key, such as a town’s name), hierarchical matching (aggregating smaller-area data to match a larger unit) or fuzzy matching (overlaying mismatched boundaries, such as crop fields and soil types). Finally, spatial analysis: once the problem is identified and the analysis’s purpose defined, GIS’s own analytical strength, chiefly overlay analysis (integrating multiple map layers, as in the Aligarh land-use case study) and buffer/proximity analysis (as in the western Uttar Pradesh hospital case study), is used to transform the linked database into information that is actually useful to decision-makers.
5 Case Studies
(A) 1 mark Name the five components of GIS mentioned in the passage.
Answer: Hardware, Software, Data, People and Procedures.
(B) 2 marks What does the ‘Software’ component of GIS comprise, per the passage?
Answer: Modules for data entry, editing and maintenance; for analysis, transformation and manipulation; and for data display and output.
(C) 2 marks Why is the ‘Data’ component called the backbone of GIS, and how may it be obtained?
Answer: It is called the backbone of GIS because spatial and tabular data are what the whole system organises, links and analyses; without them there is nothing for the other components to work on. Data may be acquired from an outside supplier or created/collected in-house by the user.
(A) 1 mark What is a buffer, as described in the passage?
Answer: A zone of a specified distance created around a point, line or area feature.
(B) 1 mark What is this kind of analysis called?
Answer: Proximity analysis.
(C) 4 marks Describe the western Uttar Pradesh buffer case study described in the passage, and state its conclusion.
Answer: Buffers of 2, 4, 6, 8 and 10 km were mapped around six western Uttar Pradesh cities with major hospitals, namely Saharanpur, Muzaffarnagar, Meerut, Ghaziabad, Gautam Budh Nagar and Aligarh. The conclusion was that areas closer to these cities are better served by hospital facilities, while people living farther away, outside the smaller buffer rings, have to travel longer distances to access medical services and are the least benefitted.