Data abstraction and Spatial Data models

Question 1

What is a model?

Answer 1

Represnetation of something
simplification of the real world or reality.

Question 2

What is a data model?

Answer 2

an abstraction of something else.

Question 3

What is a spatial model?

Answer 3

abstraction of spatial phenomena on the earth’s surface.

Question 4

What is data abstraction?

Answer 4

representation of the real world in a simpler form on a digital format.

Question 5

What are the 2 General models?

Answer 5

Vector and Raster models
Vector = point, line, polygons.
raster = grids and pixels.

Question 6

Explain the different Vectors.

(discontinuous/discrete)

Answer 6

points = buildings, or important locations, boreholes.
lines = roads, rivers, streams, railways etc.
polygons = areas, water bodies (dams, resevoirs). agriculture orchids, forests, vegetations, sand dune, nature reserves.

Question 7

What is a feature layer?

AKA vector layer

Answer 7

Depicts a common theme.

Question 8

What are the important file extentions?

Answer 8

Primary Files:
.shp
.dbf
.shx

Question 9

What is raster data?

(continuous)

Answer 9

Grid cells and pixels organised into rows and columns.

Question 10

What is remote sensing?

Answer 10

collecting data without actually getting in touch with the physical thing.

Question 11

What are the raster model types?

Answer 11

Integers, represents discrete data - roads, rivers and land cover.

Floating points, decimals, continuous data - elevation and rainfall.

Question 12

what spatial resolution?

Answer 12

size in m/km/cm of each individual pixel representative of the actual distance on the gound
smaller resolution - finer
bigger - coarser.

Question 13

High Spatial Resolution

Answer 13

▪ Small grid cells (pixels)
▪ Fine scale
▪ Lots of pixels
▪ Large file sizes

Question 14

Low Spatial Resolution

Answer 14

▪ Large pixels
▪ Coarse scale
▪ Fewer pixels
▪ Smaller file size

Question 15

How can raster data be represented?

Answer 15

3D and 2D

Question 16

What are the common raster 3D models?

Answer 16

TERRAIN MODELS (TM)
* Digital Terrain Model (DTM) = Digital Elevation Model(DEM) – Terrain height
* Digital Surface Model (DSM) – Surface height including artificial structures

TRIANGULATED IRREGULAR MODEL (TINs)
* Both were designed to simulate real world entities e.g., valleys,
peaks, slopes, & stream channels
* most surfaces can be represented in either model

Question 17

Raster coding

Answer 17

Real world (or a vector map)
Divide the world \ study area into a series of grid cells (pixels)
Use majority rule to decide how each pixel will be coded – what single attribute will be assigned