Spatial Information Technology, Class 12 Practical Geography

What Spatial Information Technology is about

Key concepts

Spatial information technology and GIS

NCERT section What is Spatial Information Technology?; What is GIS?

Spatial comes from 'space': features spread over a definable geographic area with measurable dimensions. Most data today have a location component, such as the address of a municipal office or the boundary of a farm.

Spatial information technology is the use of technology to collect, store, retrieve, display, manipulate, manage and analyse spatial information. It combines remote sensing, GPS, GIS, digital cartography and DBMS.

GIS: made possible by computing advances from the mid-1970s. It is a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data referenced to locations on the Earth, usually a spatially referenced computer database plus application software. It joins computer assisted cartography and DBMS, and draws on computer science, statistics, cartography, remote sensing, geography, geology, hydrology, agriculture, resource management, environmental science and public administration.

Spatial and non-spatial (attribute) data

NCERT section Forms of Geographical Information

• Spatial data have a location and appear in three forms: positional (point), linear (line) and areal (area). They must be registered to an accepted coordinate system and coded to be stored in a GIS. They are the most important prerequisite of a GIS.
• Non-spatial (attribute) data describe the spatial features. NCERT's Box 4.1 contrasts a cycle shop's stock register (parts that could be anywhere: non-spatial) with a table of literacy by state (each state has a definite map location: spatial, usable in GIS).

Building spatial data in a GIS: (1) buy digital data from a supplier; (2) digitise existing paper (analogue) maps; (3) carry out your own surveys.
The choice depends on: the application, the budget, and the data structure (vector or raster).

The commonest source is topographical or thematic maps, paper or digital, which have a definite scale, symbols and colours for attributes, and an agreed coordinate system.

Advantages of GIS over manual maps, and its components

NCERT section Advantages of GIS over Manual Methods; Components of GIS

Limits of paper maps: information is processed and shown in one fixed way; a map shows one or a few predetermined themes; any change needs a new map to be drawn.

GIS advantages (data are stored separately from how they are shown, so they can be viewed in many ways):
1. Users can query a feature on screen and get its attribute data.
2. New maps can be produced simply by querying or analysing the attribute data.
3. Spatial operations like polygon overlay and buffering create new information from the combined database.
4. Different attribute items can be linked through a shared location code.

Five components of GIS:

• Hardware: processing, storage, display, input and output sub-systems.
• Software: modules for data entry, editing and maintenance; analysis, transformation and manipulation; display and output.
• Data: spatial data and linked tabular data are the backbone; the digital map is the basic input.
• People: engineers, resource and environmental scientists, policy-makers, monitoring and implementing agencies.
• Procedures: how data are retrieved, input, stored, managed, transformed, analysed and output.

Raster and vector data formats

NCERT section Spatial Data Formats; Box 4.2

Raster: a feature shown as a grid of square cells (pixels), like graph paper; each cell has a position (row, column) and a value. Resolution relates cell size to the number of cells; bigger cells lose detail.

• Used for: aerial photos, satellite images, scanned maps; low cost; when individual features need not be analysed; backdrop maps.
• Advantages: simple structure; easy, efficient overlay; compatible with satellite imagery; represents high spatial variability well; easy to program; same grid for many attributes.
• Disadvantages: uses a lot of storage; errors in perimeter and shape; difficult network analysis; inefficient projection changes; information lost with large cells.

Vector: a feature stored as points with coordinates (X, Y, or X, Y, Z). Lines and areas are built from ordered points; lines have a direction; polygons are built from points or lines; vectors can store topology. Manual digitising is the best vector input.

• Used for: high-precision work; when file size matters; analysing individual features; storing descriptive information.
• Advantages: compact structure; efficient network analysis and projection change; accurate map output.
• Disadvantages: complex structure; difficult overlay; represents high variability poorly; not compatible with satellite imagery.

Example: a diagonal line on paper is a chain of filled cells in raster, but just the start and end coordinates in vector.

Sequence of GIS activities: input, editing and conversion

NCERT section Sequence of GIS Activities; Data Verification and Editing; Data Conversion

Sequence: (1) spatial data input, (2) attribute data entry, (3) verification and editing, (4) linking spatial and attribute data, (5) spatial analysis.

(a) Buying digital data: saves time and the cost of digitising, but check compatibility: scale, geo-referencing system, collection and sampling methods, quality, classification and interpolation methods, size and shape of mapping units, and length of record. Data crossing administrative boundaries (inter-district or inter-state) are especially prone to mismatch.

(b) Manual input: enter spatial data, enter attribute data, verify and edit, and link the two. Spatial data go in by digitisation or scanning.

• Scanners turn paper maps into raster images using charge-coupled devices (CCDs), which convert light into electrical counts recorded as digital values. Maps lie on a flat bed or a rotating drum; large maps are fed past a fixed camera. Scanned images carry the original's smudges and defects, which must be cleaned.
• Attribute data (e.g. a road's width, surface, traffic) come from records, censuses, surveys or spreadsheets.

Verification and editing: print the data on a translucent sheet at the original scale and compare on a light table, left to right and top to bottom. Errors: data incomplete or doubled (omissions, gaps in scanned lines), wrong scale, and distortion (aerial photo lens and relief effects; paper maps damaged by rain, sun and folding). Editing is interactive and can take longer than input; excess points are removed by 'weeding' algorithms; raster errors are fixed by changing cell values.

Conversion: all layers must be in the same format for analysis. Usually vector to raster (most analysis is raster-based), by overlaying a grid; raster to vector is done to reduce storage.

Linking and matching data

NCERT section Geographic Data: Linkages and Matching

Linking unrelated spatial and attribute data causes chaos, so linkage must be careful. Data sets link only when they refer to the same geographical area.

• Linkage: e.g. to find child mortality from malnutrition in a state, link a file of the number of children under 10 with a file of malnutrition deaths, then divide.
• Exact matching: two files about the same features (e.g. towns) are joined through a common key such as the town name.
• Hierarchical matching: when small areas fit inside larger ones but data are collected at different detail and frequency (e.g. land use over large areas vs land transformation over small areas), add up the small areas until they match the larger ones, then match exactly.
• Fuzzy matching: when boundaries do not coincide, common with environmental data (crop fields rarely match soil boundaries). Overlay the two layers and compute, for example, crop productivity for each soil type.

Spatial analysis: overlay and buffer

NCERT section Spatial Analysis; Overlay Analysis Operations; Buffer Operation

GIS's real strength is spatial analysis: using spatial and attribute data and models to answer real-world questions and turn data into useful information for decision-makers, even predicting trends. First define the problem and purpose. Operations include overlay, buffer, network analysis and digital terrain models (NCERT covers the first two).

Overlay (the hallmark of GIS): combine two or more thematic layers of the same area into a new layer, like sieve mapping (tracing maps over each other on a light table).

• Uses: detecting land use and land cover change between two dates, and suitability analysis for proposed land uses.
• NCERT example: overlaying Aligarh's urban land use maps for 1974 and 2001 shows land transformation and maps the city's urban sprawl.

Buffer (proximity analysis): a zone of specified distance around a point, line or area; it always produces polygons.

• Uses: finding areas or people served or denied facilities such as hospitals, medical stores, post offices, paved roads and parks; and the impact of point sources of air, noise or water pollution (e.g. households within 1 km of a chemical factory).
• NCERT example: buffers of 2, 4, 6, 8 and 10 km around cities with major hospitals in western Uttar Pradesh (Saharanpur, Muzaffarnagar, Meerut, Ghaziabad, Gautam Budh Nagar, Aligarh) show that areas near the cities are well served while distant people travel far.
• Software named in NCERT: ArcView/ArcGIS, GeoMedia, Quantum GIS (free and open source).

Spatial Information Technology in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Spatial Information Technology: key facts

Spatial information technology

Remote sensing + GPS + GIS + digital cartography + DBMS

Collect, store, retrieve, display, manage, analyse.

GIS components

$Hardware,software,data,people,procedures$

Data are the backbone.

Spatial data forms

$Point(positional),line(linear),area(areal)$

Attribute data describe them.

GIS sequence

Spatial input -> attribute entry -> verify and edit -> link -> analyse

Editing can take longer than input.

Raster vs vector

Raster: grid cells, easy overlay, satellite-friendly, big files; Vector: coordinates, compact, accurate, network analysis

Convert to one format before analysis.

Matching types

Exact (common key), hierarchical (aggregate small areas), fuzzy (overlay non-matching boundaries)

Same area only.

Analysis

$Overlay(change,suitability);Buffer(proximity:services,pollution)$

Aligarh sprawl; western UP hospital buffers.

Tricks to remember Spatial Information Technology

Short memory aids. Say each one aloud once, then use it on a question the same day.

• GIS components

  "Happy Students Do Productive Projects": Hardware, Software, Data, People, Procedures.

  Use it when: Five components.

• GIS functions

  "CS-CIMAD": Capture, Store, Check, Integrate, Manipulate, Analyse, Display.

  Use it when: GIS definition.

• Raster vs vector

  "Raster = graph paper; Vector = connect the dots."

  Use it when: Formats.

• Matching

  "Exact keys, Hierarchical sums, Fuzzy overlays."

  Use it when: Three matching types.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which five technologies make up spatial information technology?Show answer

   Remote sensing, GPS, GIS, digital cartography and DBMS.

2. 2.What are the three forms of spatial data?Show answer

   Point (positional), line (linear) and area (areal).

3. 3.Which data format is compatible with satellite imagery?Show answer

   Raster.

4. 4.What is the best way to input vector data?Show answer

   Manual digitising.

5. 5.Which GIS operation is used for urban change detection?Show answer

   Overlay.

6. 6.What is another name for buffer analysis?Show answer

   Proximity analysis.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you define spatial information technology?
• ☐Can you define GIS and list its functions?
• ☐Can you distinguish spatial and attribute data?
• ☐Can you name three ways to build spatial data in GIS?
• ☐Can you list four advantages of GIS over paper maps?
• ☐Can you name the five GIS components?
• ☐Can you compare raster and vector formats?
• ☐Can you list the sequence of GIS activities?
• ☐Can you explain exact, hierarchical and fuzzy matching?
• ☐Can you explain overlay and buffer analysis with examples?

Spatial Information Technology: frequently asked questions