W4 Flashcards
What is overlay analysis?
A GIS operation that superimposes multiple data sets (that have different themes) together for the purpose of identifying relationships between them
- it will create a new map combining the new selected themes
What does a geometric union do? Draw a diagram
computes a geometric union of the input features. All features and their attributes will be written to the output feature class
key functionalities:
- works with points, lines, and polygons
- works with any number of input layers
- attribute values from all input feature classes will be copied to the output feature class
What does a geometric intersection do? Draw a diagram
Computes a geometric intersection of the input features. Features or portions of features which overlap in all layers and/or feature classes will be written to the output feature class
key functionalities:
- works with points, lines, and polygons
- works with any number of input layers
- input and intersect features can be of different geometry types
What does the erase function do? Draw a diagram
Creates a feature class by overlying the input features with the polygons of the erase features. Only the portions of the input features falling outside the erase features outside boundaries are copied to the output feature class
Key functionalities:
- works with points, lines, and polygons
- erase feature must have an equal or higher geometry dimension than Input features
What does symmetrical difference do? Draw a diagram
Takes input features or portions of the features and update the features that do not overlap and write them to the output feature class
Key functionalities:
- the input and update feature class must be of the same geometry type
What does clip do? Draw a diagram
Cuts out a piece of one feature class using one or more of the features in another feature class as a cookie cutter
Key functionalities:
- works with points, lines, and polygons
- similar to intersect except it does not store the attributes of the clip features
What does Identity do? Draw a diagram
Computes a geometric intersection of the input features and identity features. The input features or portions thereof that overlap identity features will get the attributes of those identity features
Key functionalities:
- input features can be points, lines, and polygons
- identity features either must be polygons or have the same geometry type as the input features
What does the update tool do? Draw a diagram
Computes a geometric intersection of the input features and update features. Updates the attributes and geometry of the input features to create the output feature class
Key functionalities:
- works only with polygons
- input feature class and update feature class field names must match otherwise they will be removed
What is map algebra (cartographic modelling) (raster data)
Simple, powerful algebra that utilizes a variety of tools, operators, and functions to preform geographic analysis using raster data
- uses mathematical functions to manipulate geographic data to obtain desired information
- cell by cell combination of raster layers using mathematical operations
What are boolean operations in the context of raster data?
Logical operations where in the raster value 0 means false and the value 1/everything else means true
When computing raster data calculations how do arithmetic operators function? What are some examples of arithmetic operators?
Apply operation to every grid cell
- call be applied between grids (ex. a+b) or to transform a single grid (ex. a+273)
- +,-,*,/,^
When computing raster data calculation how do relational operators function? What are some examples of relational operators?
do evaluation of a condition for one grid (ex. A<9) or a comparison between two grids
- gives an output of 0=false, 1=true
- <,>,==,…
