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Fundamentals of GIS > GIS Final Exam > Flashcards

GIS Final Exam Flashcards

1
Q

What does a raster model do?

A

It uses an array of values in cells/pixels representing squares on the ground

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2
Q

What does the cell value correspond to?

A

the characteristic of the spatial phenomenon at the cell location

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3
Q

What is raster data BEST suited for representing?

A

Continuous Phenomena

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4
Q

What is a corner cell assigned with:

A

X-Y Coordinate pairs.

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5
Q

What do columns represent in GIS

A

X coordinate

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6
Q

What do rows represent in GIS

A

Y coordinate

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7
Q

What does cell size determine?

A

The resolution of a raster

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8
Q

What does it mean if the cell size is smaller?

A

The resolution is higher

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9
Q

What is required if the cell size is smaller and the resolution is higher?

A

More cells are required to cover the same area, requiring a larger file size

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10
Q

What does each cell contain?

A

ONE numeric value (like integers or floating points)

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11
Q

What do numeric values found in cells correspond to?

A

One specific characteristic or spatial phenomenon

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12
Q

What are the advantages of raster?

A

-provides a simple data model
-makes for easy data collection
-is better at analyzing certain types of data
-often has faster analysis than vectors
-imagery is desirable for certain maps

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13
Q

What are the 3 types of raster data

A

Thematic, images, and indexed color raster

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14
Q

What is continuous raster?

A

Presents quantities/variables that change over the earth’s surface (precipitation, elevation, population density, temperature etc.). This means that neighboring cells often have different values to show continuous change over space.

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15
Q

What does a discrete raster do?

A

Stores vector type features in a raster format. This means that neighboring cells usually have the same values, but they can change suddenly at the borders.

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16
Q

What format are cell values usually in in a discrete raster?

A

Integer

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17
Q

What is an image raster?

A

A raster that stores reflectance of electromagnetic radiation from earth’s surface as its values.

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18
Q

What is a raster pyramid and why is it needed?

A

They are a way for a raster to speed its display. It takes little time and increases the storage size by about 50%.

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19
Q

What is raster resampling?

A

The process of recalculating and assigning the cell size/orientation of a raster.

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20
Q

What is block resampling?

A

Category values (majority, central cell), numeric values (average, medium, minimum),

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21
Q

in GENERAL RESAMPLING, what is the nearest neighbor method?

A

uses the value from the original cell falling at the center of the new one

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22
Q

in GENERAL RESAMPLING, what is the area-weighted average

A

area-based averaging of the involved
original cells

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23
Q

in GENERAL RESAMPLING, what is the bilinear interpolation

A

distance based averaging of the 4 nearest original cells

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24
Q

in GENERAL RESAMPLING, what is the cubic convolution?

A

weighted avg of the 16 nearest original cells.

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25
What are the 2 parts of the raster file:
Header and Number array
26
What is the header in the raster file?
provides the information about the file, such as the number of rows and columns, coordinate system
27
What method is used to reduce raster storage size?
Compression
28
In raster compression, what is the lossless method?
Includes run-length encoding and quad trees.
29
What does the run-length method of the lossless method do?
stores the number of cells and the cell value of each run?
30
What does the quad tree method of the lossless method do?
divides the area, step by step, into quadrants until it becomes homogenous with each quadrant. See the spatial indexing system on the first file.
31
What is implicitly stored in a raster?
Location information
32
How many times should projecting raster be done, and why?
As few times as possible. It takes more memory and may introduce artifacts.
33
How is a georeferencing raster done?
-Scanned maps have a cs in pixels and must be georeferenced -Users identify pairs of ground control points visible in the raster and in a reference dataset -a transformation then calculates the real world coordinates from the control point pairs and applies it to the raster.
34
In georeferencing, what is an affine transformation?
Linear transformation involving translation, rotation, scaling, and shearing
35
What is the MINIMUM number of points that affine transformation requires?
three
36
In georeferencing, what is a second/third order polynomial?
-It allows stretch or contact -Additional points are needed
37
Does raster data explicitly store x-y coordinates for every cell?
No
38
What does raster overlay do?
Applies cell-by-cell operations on a stack of aligned cells to conduct the analysis.
39
What does map algebra do?
combine 2+ layers to produce a new raster layer.
40
What are some map algebra operations?
Arithmetic functions, statistical functions, boolean operations, etc.
41
How are Rasters first converted to boolean rasters?
Via logical functions for boolean overlay operations
42
What are the ONLY possible values for a boolean raster?
True or False
43
How is raster boolean overlay performed?
On a cell-by-cell basis
44
What happens in a weighted overlay?
-Input rasters (R) are ranked, which have scaled values and represent different conditions. -A weight (W) is then assigned to each raster to indicate its relative importance. The weights must sum to 1.
45
Where do local operations process?
On a single cell from each raster at a time
46
What does a neighborhood (focal) operation use?
A focal cell and a set of its surrounding cells for the calculation
47
where do zonal operations apply
to a zone defined by a group of cells of the SAME values.
48
What does a global operation do?
Performs a computation on the raster as a WHOLE.
49
What can a global operation do?
Measure physical distance, allocation and direction.
50
What mathematical functions can be used in a local operation?
Arithmetic, logarithmic, trigometric, etc.
51
In a LOCAL operation, what does reclassification do?
Creates a new raster by classification
52
What is spatial interpolation?
The process of using points with known values to estimate values at other points.
53
the number and distribution of sampling points can influence:
The accuracy of spatial interpolation
54
What does systematic sampling look like?
Even distribution/even rows
55
What does random sampling look like?
Random dots
56
What does adaptive sampling do?
Makes the dots cling to object
57
What is tobler's law?
Everything is related to everything else, but near things are more related than distant things
58
One common interpolation method is IDW. What does it stand for?
Inverse Distance Weighted.
59
What does Inverse Distance Weighted interpolation do?
Gives greater weights to points closest to the prediction location, and the weights diminish as a function of the distance.
60
What does Inverse Distance Weighted interpolation do?
Gives greater weights to points closest to the prediction location, and the weights diminish as a function of distance. A specified number (or all) points can be used to determine the output value for each location
61
What does the spline method do?
Estimates values using a mathematical function that minimizes overall surface curvature, resulting in a smooth surface that passes exactly through the input points.
62
What is the spline method best used for?
Gently varying surfaces like elevation, water table heights, or pollution concentrations
63
How is IDW method different from spline method
In IDW, the contour lines are LESS smooth, and the peaks and valleys form at extreme values in the same sample data.
64
What is density estimation?
A function that counts the number of features within a specified circle and divide by the circle area to yield a density value.
65
What is a simple density function?
Function that assumes that the weight value occurs exactly AT THE FEATURE LOCATION
66
What does a kernal density function do?
Spreads the value over an area using a distribution function before counting?
67
Slope is a surface analysis tool. What does it do?
Measures the rate of elevation change at a surface location
68
What are the two forms that slope can be reported in?
Degree or percent
69
What is the aspect of a slope?
the direction of the steepest slope
70
How is aspect expressed
In an azimuth angle from 0 to 360, where North= 0, and flat areas are assigned a value of -1
71
What does a Hillshade analysis tool do?
Depicts the brightness of terrain reflections given a terrain surface and an illumination source that is placed at a designated azimuth and zenith angle
72
what does a viewshed do?
Shows the areas that are visible from a set of designated observation points
73
What does the cut and fill analysis tool do?
Determines HOW MUCH material is LOST OR GAINED in a study area by comparing two surface models of the area. One before a change and one after the change.
74
What does editing refer to in GIS?
Updating existing feature classes, or creating new ones, including BOTH spatial AND attribute information
75
What are some editing tools to maintain topology?
Snapping to avoid dangles: point endpoint, edge, and vertex snapping. -and creating coincident polygon boundaries: autocomplete polygon construction tool and split tool
76
Sketches:
Provisional features used when creating or modifying shapes in ArcGIS pro.
77
Map topology:
Construct in arcgis to automatically track features that are adjacent or connected to each other.
78
In Sharing GIS, what is a workflow?
A sequence of data management or analysis steps needed to complete a task.
79
What are the 3 ways to share workflows in ArcGIS
ModelBuilder Scripts Tasks
80
What does modelbuilder do?
A graphic canvas used to string tools and inputs in a sequence for automatic execution
81
What is a script?
Programs written in computer languages
82
What is a task?
Workflow that permits a user to make decisions/interact with the workflow as needed.
83
What is metadata
Data about data.
84
What defines quality data?
The fitness of a dataset for a given purpose
85
One data quality issue is lineage. What is its definition?
Where did it come from, and how was it processed?
86
One data quality issue is positional accuracy. What is its definition?
Are features in the right location?
87
One data quality issue is attribute accuracy. What is its definition?
Are the attributes in the table correct?
88
What is logical consistency?
How well are the real-world relationships configured in the data.
89
One data quality issue is completeness. What is its definition?
Was every instance recorded or every measurement taken>
90
One data quality issue is temporal accuracy. Definition?
How long will the dataset remain valid, and are there any regular updates planned?

Fundamentals of GIS (6 decks)

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