GIS FINAL Flashcards
Continuous Surface?
A surface with continuous values that can be changing
Object? Are they discrete or continuous
Items on a data model
What is Data Model?
Set of information that makes a model of the world
What are 3 types of objects?
Line, area, point
Examples of continuous surface?
Precipitation, elevation, temperature
Diff between simple & complex line?
One is straight, other has turns/changes direction
Diff between polygon & connected polygon?
One is composite, one is homogenous
What is vector data model?
Assembly of polygons, lines and points of varying shapes where each represents one or more objects
What is a raster data model?
Assembly of pixels (grid)
What are the diff types of tables?
Feature attribute table, stand alone table
What is feature attribute table?
Stores attributes of vectors and contains spatial information of the vectors
What is stand alone table?
Table w/ no spatial information and consists of any data
What are the 4 diff data types?
Integer, text, double, float
What are the hexarchies of attribute levels
Nominal, Ordinal, Interval, Ratio
Def of each attribute level?
Nominal: distinct objects
Ordinal: has hierarchy (order)
Interval (has a range-often in the decimals) but no true 0
Ratio: balanced around a true 0
What is difference between short, long, float, double?
short: 2 byte integers
long: 4 byte integers
float 4 byte integers
double: 8 byte integers
Convention for naming?
letters & numbers & underscores, no spaces
What are the names for column, row and intersection?
attribute, tuple, relation
Diff between primary and foreign key?
Primary is linked directly to a tuple, foreign links data from another table to the primary
What are the 4 relationships?
one to many
many to one
many to many
one to one
Is join temp or permanent
temp
diff between relation and join?
relation highlights/selects from both tables, join brings the two tables together
What are pros of vectors vs discrete?
Discrete info, saves storage ,topology can be applied, many attributes for one feature
Pros of raster?
Discrete & continuous info, easy overlay, easy to build from sensor information, uniform size
What are characteristics of arc?
nodes, line segments, verticies
Simple vs complex polygon?
complex has more polygons within it
What is topology?
allowing features to have spatial relationships with one another (i.e where a line is respective of another)
What are the 4 types of spatial relationships?
Containment (is it within?), adjacency (what is it next to?), intersection (is it sharing a location with anything else?), connectivity (is it connected to another linear feature?)
Types of data models for storing points/coordinates?
Spaghetti: (lists of coordinates)
Node/Point: (table of where each node is)
Arc: (table of start node [Fnode], finish node[Tnode], verticies, and what polygons are to the left and right of it)
Polygon: (lists line segments/arcs)
What are the 4 raster formats?
JPEG, GIF, BMP, TIF
How are rasters stored?
every cell is referenced from grid origin which is at the bottom left corner. When called, cell center location is referenced
What is GSD?
Ground sampling distance, tells us how much distance each cell in a raster represents.
Is larger GSD better or lower GSD?
larger GSD means more area is covered per cell, smaller GSD means more precise
What are the 4 broad categories of rasters? What do each mean?
Image (values represent sensor objects/energy), thematic (data represent integer values of a category/class), interpolated (continuous usually values), and their following derivatives (slope, classification, zonal, aspect)
What are ways to encode raster data?
Sequential (in order, one line)
Run length (starts at beginning of each line) and combines repeated values into 2B,3B etc
Row Order (zig zag, always starts at start of each line)
Row Prime Order (horizontal U shape, starts at beginning then starts at end of next row)
Quadtree (separates data into 4 quadrants repeatedly until all targeted boxes are homogenous or max storage is used
What is a query?
Selects polygons/features for selective questioning
What are the 3 diff kinds of queries?
Attribute, spatial and interactive
What is an interactive query?
Selects spatial features via a lasso/shape/clicking the feature
What is attribute query?
Selects features based off of their attributes (many)
What is spatial query?
Selects based off of relationships between two feature classes (within distance, in distance etc)
What is a buffer? What is it used for?
Adds extra space put around a feature (points, lines polygons). Used to find gaps in coverage, areas within certain distance of road…
Difference between individua buffer vs dissolved buffers?
Individuals show overlapping, dissolved just merges overlapping into one shape
What is erase tool?
Erase fully eliminates all features within an area
What is clip tool?
Makes the map into a desired shape (think of making a rectangular map a circle shape to fit onto slideshow)
What is Ian McHarg’s technique for overlaying layers?
Overlays 2 layers with part of the same spatial reference and contain all attributes from both layers
What are the 5 different overlay tools and what do they do?
Union (keep all), intersect (keep only overlapping part), identity (keeps all of first shape + overlapping part of second and its attributes, symmetrical difference (keeps non intersecting parts), apportion polygon (overlays attributes from first onto second target polygon)
What is spatial join?
Joins attributes from one spatial feature on one layer to a diff spatial layer on a different layer (aka joins two different feature layers w/ different data into one)
What is aggregation?
Groups spatial features together and dissolves them to make one whole new feature class (which can tell us a summary sum, mean, STD, median etc)
What are the 4 raster function types?
Local (cell), neighbourhood (around cell), zonal (a zone), global (everything)
What does reclassification do?
Creates new raster layer with changed attribute values that still mean the same thing (i.e making 0 be NODATA)
Types of reclassification?
Binary masking (making everything 0s and 1s)
Classification reduction (making new values that mean the same thing, cleans it up)
Changing measurement scales (Adding ranks/order to data)
What does XOR mean?
exclusive or, only shows parts that are one or another and not both
What is focal function? what is block function? In neighbourhood functions
block function does something within a stationary non overlapping area
Focal function does something within an overlapping area centered around a specified point
What is aspect?
Direction that the higheest slope faces in a raster region
What do zonal functions do?
They are functions that create one output layer by figuring out where cells from one layer fall into the cells of another layer to get multiple attributes into one cell
What is a zone?
Zones are cells with identical values that do not need to be connected
What is global function?
A function that is applied to everything
What is distance function?
Measures either weighted o Euclidean distance from a defined starting cell.
What are 2 ways of collecting data?
Capturing and transfering
What are 4 different ways of collecting raster data?
Satellite Imagery, drone, LIDAR , Aerial photograph
What is raster conversion? In secondary raster capture
Converting maps for other uses for raster/gis uses through scanning
How do you georeference a raster?
Add to desired coordinate system, overlay one another, add ground control points (corners) and adjust geometric shape as necessary
What is RMS error?
error between estimated and actual locations of the ground control points (if ground control point is off, entire thing is off by a certain amount)
How to collect vector data?
GPS surveys, field surveys (getting someone to walk a road with a tracker), Lidar (converting from raster to vector)
How do we assign fixed locations on Earth to map everything else around?
24 satellites orbitting earth with many master control stations around the world. Our locations are based off of closest satellite position and may differ depending on coverage and interference.
How to convert vector data?
Digitizing (coordinates converted to digital format)
Can be manual via tables and a tool where they trace the physical map
What is snapping? What are the different types of snapping?
Snapping is linking two lines together within a certain predetermined distance. Vertex (middle), edge (along the line), end (one of the ends of the line)
