Key Terms Flashcards
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.
Segment Function
Allows creating lines with clicks, each click adds a row to an attribute table.
Interactive Attribute Tables
Attribute tables are not interactive; recalculations are needed if paths are changed.
Spatial Analysis
Spatial analysis is like solving puzzles with maps. It’s a way of examining geographic patterns and relationships to uncover insights about the world around us. It helps us understand how things are connected in space and how they change over time.
Queries in Spatial Analysis
Queries in spatial analysis are like asking questions about maps. They help us find specific information or patterns within geographic data. By asking the right questions, we can uncover valuable insights about locations, relationships, and characteristics of features on the map.
They can be requests to select features or records from a database which are often expressed as statements or logical expressions.
Aspatial Queries
Concerned with attributes within the database table, regardless of spatial information.
Spatial Queries
Focus on location, distance, and other spatial properties visible on the screen.
Query Results
Typically return 1 for true and 0 for false for both Raster and Vector data.
Combining Queries
Queries can be combined between layers to refine results
Query Outputs
Output of a GIS query is usually a map.
Final answers are generated by combining layers where both conditions are true.
Spatial Query2
A statement or logical expression that selects geographic features based on location or spatial relationship. For example, a spatial query might find features, which intersect, touch, or cross another feature.
Map Overlay
Geometric intersection of two or more datasets to combine, modify, or update features in a new output dataset.
Different types of overlay can yield different results for vector and raster data.
Vector Overlay
Overlays polygons from one layer over polygons from another layer, using Boolean terminology.
Changes or cuts can alter the attribute table.
Vector Overlay Types
Intersection: Computes the geometric intersection of input features, retaining areas where both conditions are true.
Clip: Extracts features from one layer that lie entirely within a boundary defined by features in another layer.
Raster Overlay
Combines pixel or grid cell values in each data layer using Boolean, arithmetic, or relational operators to create a new composite layer.
Resolution impacts data size; doubling resolution quadruples data size. Understanding
the resolution is crucial.
Map Algebra
Involves using maps as variables in equations to combine data layers using mathematical, logical, or Boolean operators, creating new data layers.
Types of Operators
Mathematical: Perform arithmetic operations.
Boolean: Evaluate true or false conditions.
Relational: Assess specific relational conditions (outputs true as 1, false as 0).
Raster Calculator
Tool allowing the use of maps in calculations, as rasters are composed of numbers.
Local Operations
Applied cell by cell, requiring both layers to be of the same size.
Global Operation
Applied from the perspective of each cell, affecting values across and down but not diagonally due to differing distances.
Focal Operations
Change cell values based on their neighboring cells, such as calculating slope.
Map Subtraction
Subtracting one map from another reveals differences, useful for calculating changes such as temperature fluctuations on a planet.
Map Algebra Realtional
Use the rastor calculator to find out if somehting is sutiable = it will change the map w colours output w t or f
Reclassification
Process of inputting values and deriving new output values.
Involves replacing input values with new raster cell values.
Often used to simplify or alter the interpretation of existing raster data.
Can be applied to both raster and vector data.
Simplifies or classifies results, serving as an answer to a query.
Example: Creating a table in Excel and inputting values for reclassification.
Automatic Data Classification
For more complicated statisitics
Useful for many classes in one feature file (when it is practically not possible to manually classify into groups).
Typically used for raster
Requires classification schemes (algorithms or mathematical formula) which will combine various classes into a single group.
Classification Using Statistics
data presented in a different way that can cause different results
Equal-interval Classification
Natural Breaks Classification
Quantile Classification
all three methods give different interpretations without corrupting the data
Equal-interval Classification
A data classification method that divides a set of attribute values into groups that contain an equal range of values. = more intuitive but ‘ doesnt respect the data’
Natural Breaks Classification
A method of data classification that partitions data into classes based on natural groups in the data distribution. Natural breaks occur in the histogram at the low points of valleys. = harder to communicate but better for statisitics
Quantile Classification
A data classification method that distributes a set of values into groups that contain an equal number of values. = uses the data with fixed intervals but the intervals are based on the number of values within that class
Vector classification using vector
Classifying vector data involves assigning various symbols to features (different objects within the same layer) based on their attributes. This makes it easy for map users to visually understand the attributes of different features.
Neighborhood functions / proximity analyses
Analyzing the relationships between an entity and its surrounding entities or attributes involves examining how one entity is related to others nearby.
This is crucial because many questions rely not only on what exists at a specific location but also on what surrounds that location.
A common and effective method for analyzing these relationships is by using spatial analysis techniques.
Buffering
A zone constructed outward from an object (point or line) to a specific distance (user defined)
Setback
Definition: A zone inside a polygon constructed a fixed distance from the edge.
It’s a zone within the buffer area.
Buffers may sometimes overlap, but data from only one singular buffer is typically needed.
Each buffer represents one row; when connected, the lines dissolve together.
Often simplifies processes, such as in the butterfly project.
Important note: Once intersections are dissolved, this action cannot be undone.
Rastor Neighborhood Operations
Neighborhood operations are commonly used for data simplification on raster datasets. An analysis that averages neighborhood values would result in a smoothed output raster with dampened highs and lows as the influence of the outlying data values are reduced by the averaging process.
Focal Operations
Change a value based on its neighboring cells
Neighbourhood Statistics is a focal function that computes an output raster where the value at each location is a function of the input cells in a specified neighbourhood of the location.
Borning for one cell but useful when changing more than one cell
Moving Window
Definition: A grid pattern that processes each cell in a raster dataset by shifting across the dataset.
Usefulness: It’s handy for calculating local statistics, detecting edges, and smoothing data.
Smoothing Effect: It smooths data by averaging and reducing random noise.
Impact of Window Size: Larger windows make data coarser and increase smoothing.
Manipulation: It allows adjusting map appearance without compromising statistics, letting you confirm or challenge certain phenomena.
Low pass filter
removes the randomess when smoothing data
High pass filter
difference between the smoothed map from the original making it a map of the noice – useful for seeing if the sensor is working correctly
Topographic Functions
Definition: Utilize Digital Elevation Models (DEMs) to depict slope (inclination), aspect, and hillshading.
Methodology: These functions are typical neighborhood processes, where each pixel in the resultant layer is influenced by its own elevation value as well as those of its surrounding neighbors.
Characteristic: Essentially, they apply neighborhood functions on top of elevation models to generate information about slope, aspect, and hillshading.
DTM and DSM
DTM – ground surface with nothing else
DSM – is the ground and building with it
= rastor can be both
= Vector triangular irregular network – different kind of digital elevation model
SlopeTool
The Slope tool measures the steepest slope between each cell by considering the values of its eight neighboring cells within a 3x3 window.
Aspect Tool
Neighborhood analysis as well
The angle the slope is facing
The aspect tool calculates the compass direction that a topographic slope faces, with the aspect value for each cell in the raster calculated using an algorithm that incorporates the values of the cells eight neighbours (3 x 3 window) – usually measure in degrees.
Based on its neighbor it will respond based on the way that it is facing
Hilshading Tool
The hypothetical illumination of a surface according to a specified azimuth and altitude for the sun, which creates a three-dimensional effect that provides a sense of visual (shaded) relief
Just changes the way that we look at the map
Not statisical analysis
We create a fake sun and the shading is based on its neighbor
A good way of communicating a map without color
Viewshed Analysis Tool - 3D DEM based
The viewshed analysis tool is useful when you want to know, for example, what can be seen from one or more points.
It tells you what you can and cannot see based on where a person is standing
Spatial Intererlation
Where we have gaps in out knowledge =
e.g. a satelitte is trying to take a photo but there is a cloud
= it makes a guess on whats missing and tries to fill in the wholes
Extrapelation
Going beyond the data to guess the future
Network analysis
Using google maps to find out how far and how long it will take us to get from A to B
Can factor in traffic , road network and other layers can be included
Spatial entities
(e.g. tree, roads, habitat) can be described in terms of points, polylines and/or polygons (area). Non-spatial data (data without inherently spatial qualities such as a description) or attributes have to be stored in a tabular format, linked to these entities.
Attribute Tables
provide information and/or description of spatial entity (e.g. point = tree, polyline = road, and polygon = grass field) . - classes as a common thing – something that all the entities have in common
Field
the same thing as a colum on a table - something that all the entities will have in common
Symbolism Attribute Table
The table controls how we change the symbol
Rastor attributes
Whatever is in the value of the cell
Rastor calculator to extract attributes
Vector attribute
Can join tables to make more complicated queries
The nature of the queries you can make is based on the relationship
Layerfiles
In QGIS LAYERS can come in many filetypes but the most common are vector shapefiles and raster Tiffs. The style (display) of a layer is set manually or via an imported style guide. The style settings will be lost if you open the layer in a new project or transfer the file to another person…..but you could save the style setting and transfer that too
Fileformat rastor
Raster layers, such as IMG, GEOTIFF, and TIFF, utilize a grid-cell data structure where the geographic area is divided into cells identified by rows and columns. Note that raster data layers created within GIS are usually, but not always, permanent. IMG files may reduce file size but may also result in data loss, which is why TIFF is typically preferred.
Fileformat Vector
Shapefiles (*.shp) are used to store the geometric location, shape, and attributes of VECTOR features. A shapefile comprises a set of related files and can accommodate only one feature class, which could be a point, polyline, or polygon.
MANDATORY FILES:
*.shp: Contains the feature geometry.
*.shx: Serves as a positional index of the feature geometry.
*.dbf: Stores columnar attributes of each entity in dBase IV format, directly openable in software like Excel. These files are essential for the shapefile to function as a complete dataset.
OTHER FILES (12 in total):
*.prj: Provides projection information and the coordinate system. These are supplementary files for additional data.
Remember:
A shapefile can consist of a maximum of 15 files.
Changing a layer in the browser automatically updates related files.
When sharing a layer, ensure to include all associated file formats from the browser.
Hierarchal system
In GIS, a hierarchical system refers to the organization of geographic data into layers or levels based on their scale or detail:
Base Layers: Provide general features covering large areas.
Intermediate Layers: Offer medium-level detail for specific regions.
Top Layers: Provide the highest level of detail for specific features in smaller areas.
This structure allows for efficient data management and analysis at different scales or levels of specificity in GIS.
Root folder
In GIS, a root folder refers to the main directory where GIS data, projects, and related files are stored. It serves as the starting point for accessing and managing GIS data and workflows.
Relational System
In GIS, a relational system refers to a database management approach where data is organized and stored in tables that are related to each other based on common attributes. This model allows for efficient management, querying, and analysis of spatial and attribute data
Spatial Joins
A function that combines the attributes in two layers based on distance (one feature closest to another) or containment (one feature inside another)
Merging Layers
Merge’ combines two or more raster layers, such as merging 100 aerial photos into a single layer.
Similarly, ‘Merge vector layers’ combines multiple vector layers of the same type.
Note that ‘Explode lines’ performs the opposite action by breaking apart connected lines into separate entities.
Summary Statistics in GIS
Summary statistics can be obtained with the “purple E thing” in GIS, similar to summary functions in R. This tool allows users to calculate statistics such as mean, median, sum, minimum, maximum, standard deviation, and count for attribute data associated with geographic features.
