3: Building Blocks of GIS

Question 1

WHAT IS GEOGRAPHIC INFORMATION

Answer 1

Information about stuff on the earth’s surface
WHERE, WHAT and perhaps WHEN

Examples: landform, soil, geology, attributes, property

also… data, info, knowledge
two types: geometric vs attribute

Question 2

LIST 5 BASIC GEOMETRIC PROPERTIES OF FEATURES

Answer 2

Points, lines, polygons, network, volume

Question 3

GIVE EXAMPLES OF GIS SPATIAL MODEL TYPES

Answer 3

Raster and Vector

Data model is an abstraction of the real world, which one you use depends on what you are modelling

raster for continuous data
vector for discrete data

Question 4

GIVE EXAMPLES OF GIS DATABASE STRUCTURES (3)

Answer 4

Data Structure: how the data is stored, what does the file structure look like

Relational database model - attribute files and geographic data are stored in different files
ex: SQL structure query language used to query the data in a relational database

Hierarchical database model - like a family tree, 1 to 1 or 1 to many

Network database model - many to many but time consuming

Question 5

LIST USES FOR A DIGITAL ELEVATION MODEL

Answer 5

modelling features
visibility assessment
slope
aspect
hillshade
identify route of landslide or flooding

Question 6

What is fuzzy logic?

Answer 6

Some geographic features change so are difficult to accurately represent… ex: water level of a lake

Question 7

What is the importance of scale when representing features

Answer 7

Everything we represent in GIS is based on the scale of the data, a city could be a point at one scale or an area at another, display scale is different than the scale of data

Question 8

Two types of data to represent geographic info/features

Answer 8

Discrete - a point or separate individual objects

Continuous - a field of data with no breaks

Question 9

How is spatial data stored in Vector models?

Answer 9

Points, lines, polygons

Each point has a unique identifier, an x coordinate and a y coordinate. Attributes are linked by the unique identifier

Question 10

How is spatial data stored in Raster models?

Answer 10

Grid of cells/pixels with values, sometimes just a binary system is used to show the presence of the phenomena where 0=no, 1=yes
one attribute in each cell per layer
different layers for different attributes

Question 11

Points

Answer 11

no spatial dimensions (width or length)
has a location (x,y)
can be real or virtual

Question 12

Lines

Answer 12

has length but not width
has two locations, start and end which have coordinates
can have intermediate points if complex
can be real or virtual

Question 13

Polygons

Answer 13

just like a line but ends at the first point
has two dimensions, length and width
has perimeter and area
can be real or virtual

Question 14

What are vector models good at representing?

Answer 14

Discrete data

Socio-economic data

Question 15

What are raster models good at representing?

Answer 15

Surfaces and continuous data

elevation, temperature, air pressure, salinity, pH

Question 16

Advantages/disadvantages of raster

Answer 16

Better suited for spatially continuous data
Better for visualisations and modelling
Fast and efficient processing
Large files

Question 17

What is a DEM

Answer 17

Digital elevation model (raster)
Continuous surface of cells with elevation (height) displayed as shaded by height

Disadvantages: File size is large! Cell is averaged to might miss low or high points

Question 18

Visibility analysis

Answer 18

use DEM to see calculate the viewshed seen from a specific point (observer)
example: military use, cell towers, urban planning/landscape

Question 19

Slope analysis maps

Answer 19

calculate slope angle (degree/steepness)
or aspect (direction of slope face)
example: solar gain for solar panel or building houses oriented to the sun

Question 20

TIN Surface

Answer 20

Triangulated irregular network

an efficient way of storing 3D model (not raster) no redundant data, just collect points at critical features

creates a network of irregular triangles in which lines between points have a constant slope

Question 21

Networks

Answer 21

the connected line features with a hierarchy and sometimes also a direction
example: streams or road network
often used for routing (google maps)

Question 22

Advantages/disadvantages of Vector

Answer 22

Can represent features more accurately

Processing can be heavy/slow

Question 23

VECTOR data model

Answer 23

Best for discrete features
Location referenced in x,y coordinates
Coordinates linked into points, lines, polygons
Attributes referenced by unique ID to tables
Data comes from GPS, digitisation, LINZ

Question 24

RASTER data model

Answer 24

location is referenced by a grid cell in a matrix (rectangular array)
attribute is represented by a single value for that cell
data come from images (remote sensing), scanned maps, elevation data
best for continuous features like elevation, temperature, soil type, land use

Question 25

Data Structures… why?

Answer 25

Storage and retrieval of data
Fast searching
Repeatable results
Security levels
Multi user access
Record locking (someone else editing)
Integrity

Question 26

What is a shapefile? What kind of data structure is this used in?

Answer 26

File type .shp which codes the geography and can read the data and attributes which are linked by unique identifiers
This part of a hybrid data structure, which is made up of multiple other linked files, ex: attributes, projections, coordinates, etc. This is a standard/older method for organising data.

Question 27

What is an integrated data structure?

Answer 27

New method… A personal geodatabase .mdb with all geographic and attribute data.