Week 2 Flashcards
What are the challenges of representing the real world through GIS
world is an infinitely complex place
GIS cannot represent all of this infinite complexity
Difference between continuous and discrete when abstracting the real world–> in a way that allows us to represent geographical information
Continuous: geographic objects with no well defined boundaries that exist continuously in the landscape: land elevation, salinity, humidity, temperature, most data is continuous
Discrete: geogrpahic objects with well defined boundaries, generally consisting of points, lines and areas: cities, rivers, bodies of water, buildings
What type of data is continuous and discrete fields usually used for
Continuous: interval or ratio data
discrete: nominal (categorical) or ordinal (ordered categories) data
What is a data model
A data model is a set of constructs for representing objects and processes in the digital environment of a computer.
They define how real-world spatial features are representeed in a GIS
cycle: real world–> gis data model–> operational gis–> people
What are the components of a data model
reality–> conceptual model–> logical model–> physical model
this is a flow chart showing a further obstruction of the real world - from human orientated to compute orientated
What are the two types of GIS data models and what is the difference between them
Raster and Vector data models
Raster- represented in space by an array/ grid of cells. A raster layer contains cells arranged in rows and columns. Most useful for representing continuous fields
Vector- most common form of map. Uses points, lines and polygons to represent spatial features. Most useful for representing discrete objects
What are the four types of raster data (layers)
Base layers- aerial photographs
Thematic layers- land use (represent discrete objects)
Surface layers- elevation, temperature, air pressure
Attributes of features- geotagged photographs
What is attribute data and the two types
Attribute data is qualitative data that can be counted for recording and analysis e.g. spatial attributes and non-spatail attributes
What is topology
Topology is the geometric characteristics that do not change under transformation
What are the 3 elements of topology and what are they
Adjacency: two polygons next to each other
Connectivity: two lines connected to each other
Containment: polygon A within polygon B
What is georefrencing and some examples
Concerned with identifying where geographic features are on the earth’s surface. They should be unique and constant throughout time. Examples include addresses, place names, coordinate reference systems
What are the two types of longitude
Geocentric longitude and geodetic longitude
What is a projected coordinate system
Transforms a three-dimensional geographic coordinate system to flat coordinate system
what is a plate care projection
maps latitudes and longitudes directly onto x and y axes
What are the 4 types of projection
Conformal:
Equal Area:
Equidistant:
True direction:
