GIS week 5 Flashcards
(26 cards)
What is spatial analysis and modelling in GIS?
Methods to examine, summarise, and interpret spatial data, identifying patterns and interactions.
Used to identify patterns, associations, connections, interactions, and evidence of change through time and location.
1. Spatial query.
2. Spatial operations: Reclassifying maps, Overlay analysis Measuring geometry and distance, Characterising neighborhoods.
3. Spatial interpolation: Inverse distance weights and Kriging
What are the three core types of spatial analysis techniques?
proximity analysis, overlay analysis, statistical analysis and temporal analysis
What is a spatial query in GIS?
Selecting and extracting features based on attributes or location.
How does a query by attribute work in GIS?
By retrieving features that match specific attribute values using a query language like SQL.
To retrieve all features with particular attribute values from one data layer or feature class in a spatial database and display their locations in a map
e.g. ‘Retrieve all water mains installed before 2010 with a diameter less than 30cm’.
How does a query by location work in GIS?
By retrieving features based on their spatial relationship to other features using spatial operators.
Uses 11 spatial operators. equals, disjoint, intersects, touches, crosses, within, contains, overlaps, relate, LocateAlong and LocateBetween.
Usually involves two or more data layers
To identify attribute values associated with features at particular locations
What is an example of a query by attribute?
Retrieving all water mains installed before 2010 with a diameter less than 30cm.
What is reclassification in spatial analysis?
Simplifying or merging areas by grouping features with the same attributes.
What is overlay analysis in GIS?
A process of stacking multiple data layers with a common georeferencing system on top of each other so that the relationships between features at each location can be analysed.
The most common GIS operation for comparing and analysing multiple data layers simultaneously.
E.g. calculating the number of properties within a flood risk zone.
Overlay analysis can be conducted in both vector and raster
What is a vector overlay in GIS?
Combining two or more vector layers to produce new geometries using operations like union, intersection, and difference (named after the result of the combination of two layers.)
What is raster overlay (map algebra) in GIS?
superimposes at least two input raster layers to produce an output layer.
Each cell in the output layer is calculated from the corresponding pixels in the input layers
What is map algebra in spatial analysis?
A mathematical framework for performing operations on raster layers.
What is geometric and distance measurement in GIS?
Length, area, perimeter and shape. Useful for landscape metrics e.g. interaction between spatial pattern and ecological processes.
Geometric properties and distances are usually not encoded during spatial data input. GIS offers measurement functions to calculate them
How are length, perimeter, and area measured in raster data?
By using cell counts and cell sizes to estimate geometric properties.
What is buffering in GIS?
Buffering is a distance measurement tool for vector data commonly available in GIS. It creates a zone around a feature or a set of features with a specific width.
What is a physical distance surface in GIS?
A raster showing the shortest distance from a source to every other location.
Calculates the shortest distances from a location to every other location and creates a distance surface in raster form.
The concentric rings of equal distance around the source location(s), as shown for roads.
What is a cost distance surface in GIS?
A raster showing the least-cost path based on travel time, energy, or other factors.
Distance in raster can be measured as costs incurred over physical distance.
The cost-distance can be cost of travel time, energy consumption, etc. which may be affected by topography (slope, land cover, etc).
E.g., cost for constructing a highway include cost of construction and land purchase and include potential costs of environmental and social impacts
What is spatial interpolation in GIS?
Estimating values of an environmental variable at locations whose values are unknown based on a sample of locations with known values.
Apply an interpolation method to a set of points with known values to create a continuous surface
What are the main spatial interpolation methods in GIS?
Deterministic (IDW) and geostatistical (kriging) methods.
Through spatial interpolation, spatial distributions of the environmental phenomena can be approximated.
What is Inverse Distance Weighting (IDW) interpolation?
A method where nearby points influence predictions more than distant points.
IDW estimates a value of each location by taking the distance-weighted average of the values of sample points in its neighbourhood.
Explicitly assumes that things closer to one another are more alike than those that further apart.
As p increases, the weights for distant points decrease rapidly. If the p value is very high, only the immediate surrounding points will influence the prediction.
What is spatial autocorrelation?
Spatial autocorrelation means data values at locations close to each other generally exhibit less variability than data values at locations which are further away from each other (Tobler’s Law).
Positive spatial autocorrelation is when similar values cluster together.
Negative spatial autocorrelation is when dissimilar values cluster together (dispersed).
Spatial autocorrelation is an underlying assumption of IDW i.e. that closer values have more effect while further away ones have less effect
How does the power term (p) in IDW affect the interpolation?
A higher p increases the influence of nearby points, while a lower p smooths the surface.
What is kriging in GIS?
Kriging interpolates values and their probability at a specific location.
Uses input data to build a mathematical function with a semivariogram, to create a prediction surface, and then validate the model with cross validation.
A geostatistical method that provides an optimal prediction surface AND a measure of confidence in how likely that prediction will be true.
What is a semivariogram in kriging?
A graph showing how spatial similarity decreases with distance.
What does a kriging example illustrate?
How kriging builds a prediction surface based on known sample points.
