Which of the following statements with reference to raster data format is/are correct? 1. It has a simple data structure which is compatible with remote sensing imagery. 2. The relationship between cell size and number of cells is expressed as the resolution of the raster. Select the answer using the code given below.
- (a)1 only
- (b)2 only
- (c)Both 1 and 2
- (d)Neither 1 nor 2
Correct — C, Both 1 and 2. A raster divides space into a grid of equal cells and stores one value per cell, so its data structure is nothing more than a matrix of numbers. That is exactly how a satellite sensor records a scene — a rectangular array of pixels, each holding a reflectance value — which is why raster is the natural format for remote sensing imagery and why overlay operations between layers reduce to arithmetic on matching cells. Statement 2 states the resolution relationship correctly: the cell size is the ground area one cell represents, and for a given extent the cell size and the number of cells are two sides of the same coin. Halve the cell size and you quadruple the number of cells while doubling the linear resolution.
- (a)1 only — Rejects a correct statement. Resolution in a raster is defined by cell size, and for a fixed area a smaller cell means more cells; the two quantities cannot be separated.
- (b)2 only — Rejects the raster model's best-known advantage. A grid of values is the simplest data structure in geographic information systems and is the form in which satellite imagery already arrives.
- (d)Neither 1 nor 2 — Both are standard textbook properties. The known weaknesses of raster lie elsewhere — large file sizes, blocky boundaries and the loss of exact topology, none of which is claimed here.
Geographic data comes in two models. A vector layer stores points, lines and polygons with explicit coordinates and topology, which suits discrete features such as roads, plots and administrative boundaries and gives clean edges and small files. A raster layer stores a grid of cells with one value each, which suits continuous surfaces such as elevation, temperature and reflectance, and makes overlay and modelling arithmetic straightforward at the cost of blocky boundaries and larger files.
The two statements are the two facts every syllabus lists for raster, so the intended answer is that both are correct — but understand rather than memorise them. Resolution is a ground distance: a thirty-metre raster has cells covering thirty metres on a side, and a scene of fixed extent needs four times as many of them if the cell size drops to fifteen metres. That trade-off between detail and data volume is the practical reason an analyst chooses a resolution at all, and it is why Landsat, Sentinel and Cartosat products are quoted by cell size.
- A raster stores a grid of equal cells with one value per cell; a vector stores points, lines and polygons with coordinates.
- Raster suits continuous surfaces such as elevation, rainfall and reflectance; vector suits discrete features with sharp boundaries.
- Raster resolution is the ground size of a cell — a 30 m raster has cells 30 m on a side.
- For a fixed area, halving the cell size quadruples the number of cells and the storage needed.
- Satellite images arrive as pixel arrays, which is why the raster model is the natural fit for remote sensing.
Both statements in the question describe raster strengths, so both stand.
- Reading resolution as image size in pixels rather than as a ground distance.
- Assuming raster is always inferior because its edges are blocky.
- Confusing spatial resolution with spectral resolution.
A two-statement item in which both sentences are lifted from the standard list of raster properties.
For the measurement/estimation of which of the following are satellite images/remote sensing data used? 1. Chlorophyll content in the vegetation of a specific location 2. Greenhouse gas emissions from rice paddies of a specific location 3. Land surface temperatures of a specific location Select the correct answer using the code given below:
- (a) 1 only
- (b) 2 and 3 only
- (c) 3 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
What the raster grid is actually used for. Chlorophyll, emissions and surface temperature are all continuous quantities estimated cell by cell, which is precisely the kind of data the raster model exists to hold.
- practice — not a real PYQ
Which data model is best suited to representing a continuous surface such as elevation?
- (a)Vector
- (b)Raster
- (c)Topological
- (d)Relational
Answer(b) Raster — a grid of cells stores a value everywhere, which is what a continuous surface needs.
- practice — not a real PYQ
If the cell size of a raster covering a fixed area is halved, the number of cells
- (a)halves
- (b)stays the same
- (c)doubles
- (d)becomes four times
Answer(d) becomes four times — the cell count rises with the square of the linear change.