Week4: Raster-based Data structures

Question 1

In simple raster structures, there is ..

Answer 1

a 1-1 correspondence between data value, cell & location

Question 2

Raster-based data structures - Efficiency issues

Answer 2

1) simple raster-based structure inefficient in terms of data storage: regardless of the data distribution, it uses the same amount of disk space
- can also degrade data processing

Question 3

Geographic phenomena often show a degree of …

Answer 3

spatial autocorrelation: similar values near each other

Question 4

Run length encoding

Answer 4

1) Useful when there are just a few attribute values
2) Highly inefficient when there is a high degree of spatial variability in the data
3) Lossless compression method

Question 5

Raster-based structures: Efficiency issues

Answer 5

1) Efficiently store data: compression methods

2) Efficiently access/retrieve/scan data: scan order methods

Question 6

Scan order methods

Answer 6

1) Mainly concerned with performance in terms of data processing
2) Define a total order on cells of a 2D grid: assign numbers to the cells in the order they are visited
- i.e. embed a 2D space into a 1D space
3) Also called space filling curves
4) Some methods partially preserve proximity:
- two cells that are close in space are likely to be close in total order

Question 7

Scan order methods: types

Answer 7

1) Row method
2) Row Prime method
3) Morton scan method (preserves spatial proximity relatively well)
- Also, Z-buffering
4) Morton-values (Z-values)
5) Peano-Hilbert curve