A system of linear features that has the appropriate attributes for the flow of objects, such as traffic flow.
What is turn impedance?
The cost of completing a turn on a road network, usually measured by the time delay.
What is the difference between the traveling-salesman problem and shortest-path analysis?
Shortest-path analysis is about finding the path with the minimum cumulative impedance between nodes on a network; the traveling-salesman problem has the added restrictions that the route end where it began and that each stop be visited only once, although the route can begin at any of the stops.
What is allocation?
The study of the spatial distribution of resources through a network. Because the distribution of the resources defines the extent of the service area, the main objective of spatial allocation analysis is to measure the efficiency of these resources.
Give an example of location-allocation analysis.
A soft-drink distribution company wants to minimize the driving distance between its distribution facilities and supermarkets. The goal is to have all supermarkets within a 2-hour drive, or less, of the nearest distribution facility. The goal of the analysis is to match the supermarkets to the facilities such that this requirement is met.
What is the minimum-distance model?
The model that minimizes the total distance or time traveled from all demand points to their nearest supply centers; also known as the p-median location model. Along with the maximum coverage model, one of the 2 most-common models for solving location-allocation problems.
What is the maximum-coverage model?
A model that maximizes the demand covered within a specified time or distance.
What is the dynamic segmentation model?
A data model built upon the arcs of a network, it uses real-world coordinates with linear measures. Linearly-referenced data (accidents, pavement conditions, etc.) are linked to a geographically-referenced road network. The model creates a route system by associating adjacent line segments into one or more groups that have a definite linear sequence. Then, descriptive information is associated with the route system by referencing distances from the starting point of each route.
What is the difference between continuous events and linear events?
Continuous events are always present, whereas linear events are off-and-on situations.
What are 2 methods of measuring link impedance?
Physical length and travel time (based on physical length and speed limit).
What is a TIN?
Triangulated Irregular Network, a vector data model that approximates the land surface with a series of non-overlapping triangles.
What is the vertical accuracy of a USGS NED 1 arc-second raster?
C. +/- 7 to 15 meters
What is the resolution of a USGS NED 1 arc-second raster?
C. 30 meters
The maximum z-tolerance VIP (Very Important Point) algorithm is used for converting _________ to ________.
A. DEMs; TINs
B. TINs; DEMs
A. DEMs; TINs
Local first-order polynomial interpolation is used for converting __________ to ___________.
A. TINs; DEMs
B. DEMs; TINs
A. TINs; DEMs
Explain the purpose of the maximum z-tolerance
The algorithm selects points from an elevation raster to construct a TIN such that, for every point in the elevation raster, the difference between the original elevation and the estimated elevation from the TIN is within the specified maximum z-tolerance.
To create a TIN, one can use DEM, surveyed elevation points, GPS, LIDAR, and ____________ as inputs.
Line data (contour lines and breaklines)
What are breaklines?
Line features that represent changes in the land surface, such as streams, shorelines, ridges, and roads.
What 4 factors control the visual effect of hill shading?
The sun's azimuth (the direction of the incoming light)
The sun's altitude (angle of the incoming light above the horizon)
What 4 factors influence the appearance of a 3D view?
Viewing azimuth (direction from the observer to the surface, ranging from 0° to 360°)
Viewing angle (measured from the horizon to the altitude of the observer)
Z-scale (ratio between the vertical scale and the horizontal scale)
A variety of methods are available for computing
slope and aspect from an elevation grid. Summarize the ways they differ from
All methods use a 3-by-3 moving window to calculate the slope and aspect of the center cell, but they differ in the number of neighboring cells used in the estimation and the weight applied to each cell.
What are the advantages of using TINs for terrain analysis?
More flexibility with input data types
Ability to add elevation points at their precise locations (cannot be done with DEM if the feature is smaller than the DEM's resolution)
Sharper images in 3D display result if input is TINs
What is the advantage of using DEMs for terrain analysis?
Greater computational efficiency
Apart from observation points, what other 2 parameters are important in viewshed analysis?
Viewing azimuth (sets horizontal angle limits to the view)
Viewing radius (sets the search distance for deriving visible areas).
What is a flow accumulation grid?
A grid that tabulates, for each cell, the number of cells that will flow to it; based on the flow direction raster.
What is tessellation?
A partition of the plane or portion of the plane as the union of a set of disjoint areal objects.
In a Euclidean plane, what are the 3 permitted tessellations?
List at least three factors that may affect the
accuracy of slope measures from a GIS.
Resolution of input DEM
Quality of input DEM
What is the name of the operation that is the basis for viewshed analysis?
Which of the following is not a terrain data model?
E. none of the above
Which of the following 7.5-minute DEMs have a maximum RMSE (root mean squared error) of 15 meters?
A. Level 1
Which of the following parameters represent the direction from the observer to the surface in a 3D view?
B. Viewing azimuth
A hillshade map would look _____ if the sun’s angle were higher.
If you have 2 observation points in viewshed analysis, the output grid will have ____different cell values:
To create a TIN in ArcGIS Desktop, one must use:
A. 3D Analyst
Describe in your own words (no equation) how a computing algorithm derives the slope of the center cell by using elevations of its eight immediate neighbors.
As an example, Horn's algorithm applies a weight of 2 to the 4 immediate neighbors and a weight of 1 to the 4 corner cells. In the 3-by-3 window, the 3 cells in the first column of 3 cells are added together, with the middle cell multiplied by 2; from this are subtracted cells in the third column, similarly summed; to this are added the cells of the bottom row, summed in the same way, minus the cells in the top row, summed in the same way; a square root is taken of the result and divided by 8 times the cell size.
Describe in your own words (no equation) how a
computing algorithm derives the slope of the center cell by using elevations of its four immediate neighbors.
The square root of the sum of the squared difference between the cells to the left and the right of the center cell and the squared difference between the top and bottom neighbors is divided by twice the cell size.
True or false: a local operation is limited to 2 input grids.
Which of the following functions can be used for local operations?
D. all of the above
Which of the following can be used as a neighborhood in raster data operation?
D. All of the above
Which of the following statistics is more appropriate for categorical data?
A zonal operation on a single input grid produces data on the geometry of zones.
True or false: a mask grid limits analysis to cells that do not carry the cell value of No Data.
The tool for local operations in ArcGIS Desktop is called:
C. Raster Calculator
List 3 ways one can specify the area extent for analysis.
A specified grid.
An area defined by its minimum and maximum values in X and Y
A mask grid
Which local operation can assign a unique output value to each unique combination of cell values from multiple grids?
True or false: when combining rasters, the output raster will have the minimum resolution identical to the minimum resolution of the input rasters.
By default, the power of the Inverse Distance Weighting tool is
By default, the search radius of the IDW tool is __ nearest points.
Ritter's algorithm examines the z-value of _ surrounding cells.
Horn's algorithm examines the z-value of the _ surrounding cells.
True of false: for watershed analysis, the input data does not have to be a DEM.
What are the 6 steps for creating a watershed?
Identify and fill sinks
Use the filled-in sink raster to create a flow raster
Use flow raster to create a flow-direction raster
Create a source raster
Use source raster and flow raster to create watershed raster
Snap pour points to streams
A watershed is developed for each pour point by the Watershed tool
What are the 4 cost-distance measures possible?
Least accumulative cost
What is accuracy?
The degree to which information on a map or in a digital database matches true or accepted values.
What is precision?
The level of measurement and exactness of data.
Name 4 sources of error in cartography.
Assumptions/biases by mappers
Mis- or uncalibrated equipment
GIS 205 Final
Review for final exam in GIS 205 (3-dimensional analysis)