Key Terms Flashcards
Geographic and Spatial
Geographic refers to the earths surface and near surface. Spatial refers to space
Spatial Data 3
refers to information about the locations and shapes of georgaphic features in space and the relation between them.
Database
GIS is database powered – a structured collection of spatial data and its related attribute data, organised for efficient storage and retrieval.
Spatial and Aspatial Queries
In the case of GIS, a database may be queried and the output displayed as a map / image. But it is essentially: “a request that examines feature or tabular attributes based on user-selected criteria and displays only those features or records that satisfy the criteria
Model
The term model is ambiguous: it has many different meanings depending on the context. A model is a simplification of reality, a map is one such example of a model. = an abstract of reality – cannot include all the information about reality
Data Model1
GIS is based on a second type of model, known as a data model.
A data model is defined as an abstraction of the real-world:
a mathematical construct for representing geographic objects or surfaces as thematic layers, including their spatial representation, attributes, portrayal and relationships
Rasters
photographs – made up of cells
every cell does have to be the same size , but in vector depending on the point the sizes of sections can be different
Vectors
made up of points lines or polygons – a way of representing the real world
when you join the points together you will always get a triangle
Spatial Data 4
Essentially it is any data that can be mapped to provide representations of the real world for quantitative or qualitative use.
Maps
are all abstracts of reality
Spactial Data Model
Rasters, Vectors (and TINs) are all examples of a data model.
Spatial Entites
aka a representation of the real world – like a square that represents a building – how we represent the real world on a map- every entity corresponds to a role on a table !
This is a requirement of GIS because in GIS we spatially organise things
Discrete Raster
A raster that typically represents phenomena that have clear boundaries with attributes that are descriptions, classes, or categories
Continuous Raster
how we represent natural phenomena that gradually changes- Raster in which cell values vary continuously to form a surface. Values exist on a scale relative to each other. It is assumed that the value assigned to each cell is what is found at the centre of the cell.
= a way of representing the real world where we have continues change
= each cell has some kind of relationship with its neighbor
= ‘neighborood relationship ‘ - the relationship between cells
Tobler’s law
that things close together are more likely to be related
one of the only geography laws
Raster Bands
recognize that we have different kinds of bands- a singular layer is made up of different bands sometimes
Single band raster
contain a single matrix of cell values. ,Elevation Data , Grayscale aerial imagery ,Scanned maps / document
Multiple band raster
contain multiple spatially coincident matrices of cell values representing the same spatial area ,TIFFs, IMGs ,Remotely Sensed Data , Spectral Data
= need to be aware of those differences but not important to the module
Digital Elevation Model
Digital representation of topography. Represented by cell based values with a single elevation (attribute) value representing the entire area of the cell. DEMs are typically used to represent terrain relief, and can be used to derive slope and aspect.
Topology
Topology studies properties of spaces that are invariant under any continuous deformation. It is sometimes called “rubber-sheet geometry” because the objects can be stretched and contracted like rubber, but cannot be broken.
Attributes
is whatever value is in the cell (in vector the thing on the screen connects to the screen and a row on the screen corresponds to that table)
Multiple band - remote sensing
Multiband refers to something that involves or operates across two or more bands
if we collapse them together into a singular layer , continuous data into categorical data
Vector Attributes
points, lines and polygons would have to be three different layers because you can only have one type on each layer
DEM
digital elivation model – a 3D version of the world surface = can have a vector or a raster version
triangular irregular Network (TINS)
A Triangular Irregular Network (TIN) is a way to represent a 3D surface. For example, they can show complex surfaces such as slopes and elevation. These types of models use triangles, which we form by connecting points called nodes. The nodes have X, Y, and Z coordinates. Each triangle is a facet in a TIN model.
WFS – Web Feature Service
either WFs or WMS would works but WFS allows us to see the attributes as well in CGIS = the computer code from a WFS is the data that QGIS needs= a lot of the time WFS will have passwords because companies dont want people to use them
Vectorization
A new layer will be created by digitising (drawing footpath lines) over an aerial photograph of the study area. This process is known as vectorisation, meaning the conversion of raster into vector (the reverse is called rasterisation).
Snapping
Snapping involves connecting a geometric vertex or edges of one feature to another. Snapping is an important setting when editing or creating GIS data because it ensures that edges and vertices that need to be adjoining are cleanly connected.
Entity
Individual point, line or polygon (area) = vector = the thing you see on the screen
Attribute non-spatial data about an entity
if its in a table its an attribute = if its on the screen its in a table (vector)
Attribute
Raster: Value of cell (e.g. some absolute value such as elevation or the cell number refers to data in an attribute table)
Feature
the thing in the real world - A real world object encoded in a GIS database
Data layer
A dataset for the area of interest. -will only be one thing
Image
Raster data layer (e.g. photograph)
Cell
A single pixel in a raster image. (can use cell and pixel interchangeably)
Function / Operation
A data analysis procedure – the thing that we’re doing
Measurement Tool in Spatial Analysis
Allows clicking two points to measure distance between them.
Cartesian vs. Ellipsoidal Measurements
Cartesian: Assumes a flat world, suitable for small-scale measurements but inaccurate for large distances.
Ellipsoidal: Considers the Earth’s curvature, providing more accurate results for long distances.
Measurement of Areas
Can also measure areas, accuracy depends on the scale of the study.
Adding Measurement Attributes
Functions available to add measurement attribute data to layers, like adding geometry attributes.