Advanced GIS Exam 2 Complete
Solutions
What are the general features of a surface model / digital terrain model in GIS? - ANS--
accurately represents surfaces
-suitable for data collection
-minimize data storage
-maximize data handling
-suitable for surface analysis
What is a DRG? - ANS-Digital raster graphic
-a scanned & georeferenced version of USGS topographic maps
What is a DLG? - ANS-Digital line graph
-the digitized features from a USGS topographic map
What is a US Topo? - ANS-A digital topographic map series created by the USGS ti
allow multiple layers of data to be used on a map in GeoPDF file format
What is a contour? - ANS-An imaginary line drawn on a map that connects points of
common elevation
What is a contour interval? - ANS-The vertical distance between contour lines
How do terrain and scale affect the choice of contour interval on a map? - ANS--Maps
with mountainous terrain will use wider contour intervals
-Maps with flat terrain will use narrower contour intervals
-Small scale maps use wider contour intervals
-Large scale maps will use narrower contour intervals
How are contours extracted by using GIS data such as a DEM? - ANS-The DEM is
used as a source from which ti derive contours, using the surface tool set or the create
contours tool
What is a TIN? What are the features of a TIN? How does a TIN represent a model of
terrain? - ANS-Triangulated irregular network
-A terrain model formed from non-overlapping triangles that allows for unevenly spaced
elevation points
-Use points, lines & a series of non-overlapping polygons to represent a surface
-It acts as a functional surface & is considered a 2.5D model
, How are the features of a TIN stored in GIS? - ANS--The triangle number
-the numbers for each adjacent triangle
-the three nodes defining the triangle
-The x,y coordinates of each node
-the surface z-value of each node
-the edge type of each triangle (hard or soft)
-z-values stored at nodes
What is the difference between a hard and a soft breakline in a TIN? - ANS--Hard: lines
used in a TIN to inforce surface discontinuities
-Soft: Enforce lines in a TIN that do not represent discontinuities
How do breaklines affect the creation of a TIN? What does a TIN created without
breaklines lack? - ANS--The breaklines ensure that flat features like roads & streams do
not have changing elevation values when they should be flat
-A TIN without breaklines would lack defined boundaries making the model look
unrealistic
What is VIP and how is it part of the TIN creation process? - ANS--Very Important Point
& is part of the mass point process
-Finds the most important points in the TIN (highest point, lowest point, big changes) &
uses them ti build the model
What are Mass Points (in relation to a TIN)? - ANS-A set of points with z-values that are
selected in creating a TIN
What is a Delaunay Triangle and why is it important to the TIN creation process? - ANS-
A triangle that can have a circle drawn through its 3 points & not pass through any
additional points
-Important to make triangles with the most area as possible
How can a TIN be created using the Delaunay Triangulation Method? - ANS-By taking
the mass points & creating thiessen polygons equidistant around the points.
-From there Delaunay Triangulation occurs by drawing edges perpendicular to the
thiessen polygons
How is a Thiessen Polygon constructed and how is it used to triangulate the TIN? -
ANS-By taking the mass points & drawing lines equal distance around the points.
-Then Delaunay triangles are constructed by drawing edges perpendicular to the
thiessen polygons
What are the advantages and disadvantages of using a TIN to model terrain? - ANS--
Pros:
1) flexibility of data source
2) can add points
3) good display
Solutions
What are the general features of a surface model / digital terrain model in GIS? - ANS--
accurately represents surfaces
-suitable for data collection
-minimize data storage
-maximize data handling
-suitable for surface analysis
What is a DRG? - ANS-Digital raster graphic
-a scanned & georeferenced version of USGS topographic maps
What is a DLG? - ANS-Digital line graph
-the digitized features from a USGS topographic map
What is a US Topo? - ANS-A digital topographic map series created by the USGS ti
allow multiple layers of data to be used on a map in GeoPDF file format
What is a contour? - ANS-An imaginary line drawn on a map that connects points of
common elevation
What is a contour interval? - ANS-The vertical distance between contour lines
How do terrain and scale affect the choice of contour interval on a map? - ANS--Maps
with mountainous terrain will use wider contour intervals
-Maps with flat terrain will use narrower contour intervals
-Small scale maps use wider contour intervals
-Large scale maps will use narrower contour intervals
How are contours extracted by using GIS data such as a DEM? - ANS-The DEM is
used as a source from which ti derive contours, using the surface tool set or the create
contours tool
What is a TIN? What are the features of a TIN? How does a TIN represent a model of
terrain? - ANS-Triangulated irregular network
-A terrain model formed from non-overlapping triangles that allows for unevenly spaced
elevation points
-Use points, lines & a series of non-overlapping polygons to represent a surface
-It acts as a functional surface & is considered a 2.5D model
, How are the features of a TIN stored in GIS? - ANS--The triangle number
-the numbers for each adjacent triangle
-the three nodes defining the triangle
-The x,y coordinates of each node
-the surface z-value of each node
-the edge type of each triangle (hard or soft)
-z-values stored at nodes
What is the difference between a hard and a soft breakline in a TIN? - ANS--Hard: lines
used in a TIN to inforce surface discontinuities
-Soft: Enforce lines in a TIN that do not represent discontinuities
How do breaklines affect the creation of a TIN? What does a TIN created without
breaklines lack? - ANS--The breaklines ensure that flat features like roads & streams do
not have changing elevation values when they should be flat
-A TIN without breaklines would lack defined boundaries making the model look
unrealistic
What is VIP and how is it part of the TIN creation process? - ANS--Very Important Point
& is part of the mass point process
-Finds the most important points in the TIN (highest point, lowest point, big changes) &
uses them ti build the model
What are Mass Points (in relation to a TIN)? - ANS-A set of points with z-values that are
selected in creating a TIN
What is a Delaunay Triangle and why is it important to the TIN creation process? - ANS-
A triangle that can have a circle drawn through its 3 points & not pass through any
additional points
-Important to make triangles with the most area as possible
How can a TIN be created using the Delaunay Triangulation Method? - ANS-By taking
the mass points & creating thiessen polygons equidistant around the points.
-From there Delaunay Triangulation occurs by drawing edges perpendicular to the
thiessen polygons
How is a Thiessen Polygon constructed and how is it used to triangulate the TIN? -
ANS-By taking the mass points & drawing lines equal distance around the points.
-Then Delaunay triangles are constructed by drawing edges perpendicular to the
thiessen polygons
What are the advantages and disadvantages of using a TIN to model terrain? - ANS--
Pros:
1) flexibility of data source
2) can add points
3) good display
