GIS Exam 3 Questions with Verified
Solutions
Geoprocessing - ANS-G tools are commonly used tools that we normally use to prepare
data for further analysis.
Buffer - ANS-creates polygon buffers around point, line, or polygon features using a
specified distance. Used to select features in other layers. Ask a spatial question of
what features are within a certain distance of other features. Proximity analysis. Ex:
What pipelines are within 100 ft of oil wells.
Clip - ANS-features (either points, lines, or polygons) in one layer using the extent of a
polygon in another layer. Important toll to help simplify data. Helps extract only the
features needed within a study area to create a smaller, more manageable dataset.
Used this tool to clip the MergedContours layer using the StudyArea layer in the
Caprock Canyons Project
Dissolve - ANS-Used to aggregate (combine) features in a single layer based on
common attribute values. Works on polygons and line features.
Intersect - ANS-Calculates a set of new polygons based on the combination of two or
more layers. The new output layer contains all of the features present only in the
overlap of the input layers. The input features can be point, line, or polygon, but the
output will contain features with the lowest dimension (ex. intersect lines and polygons
will output lines)
Union - ANS-Calculates a set of new polygons based on the combination of two or more
layers. The new output layer contains all of the polygons present in the overlap of the
input layers, plus the polygons that exist where there is no overlap. Answers the most
basic question in geography: What is on top of what? Ex. What vegetation is on top of
what type of soils? So you can get an idea of vegetation productivity with different soil
types.
Merge - ANS-Used to combine 2 or more layers that do not overlap into one layer. Used
to combine either 2 or more point layers, 2 or more line layers, or 2 or more polygon
layers. Note that we used this tool to merge the 2 contour (hypsography) layers in the
Caprock project.
Select by Location - ANS-Selects feature in one layer based on a spatial relationship to
features in another layer. There can be several different types of spatial relationships
,between layers. These relationships include selecting features that are completely
within, or selecting features that intersect, as well as other types of spatial relationship.
Spatial Analysis in GIS - ANS-The 2 volume ESRI Guide to GIS Analysis describes 11
basic types of spatial analysis that can be accomplished with a GIS. The following are
ex. of each of these Spatial Analysis capabilities. Can be used to do 11 different things.
Basic Measurement - ANS-Can use the basic Measure tool or the Point Distance tool in
the ArcToolbox. a.) distance: distance between point features, distance between line
features, distance between polygon features, or any combination of the above. b.)
length: dist. along a line feature -Calculate the distance along a road, pipeline or stream
segments, perimeter of a polygon - calculate the length of fenced needed to enclose a
pasture c.) area: area of a polygon or multiple polygons-calculate the total area of a
lake, or land use types in a city, county or state. NOTE: If you import a shape file to a
geodatabase, ArcGIS automatically calculates a length and area field: for a line layer,
the length-field value is the length of each line feature, for a polygon layer, the area-field
value is the area and the length-field value is the perimeter, the values calculated in
these length and area fields are based upon the units of the projection, if the layer is
unprojected, the length and area values are decimal degrees (which is meaningless), if
the layer is projected, the length values will be in meters or ft and area values in m
squared or feet squared.
Import Data - ANS-- we can also import data into ArcGIS (using tools in ArcToolbox)
- import implies that we have to go through a file conversion process
- since Geodatabases store GIS data very efficiently we can import:
1) shapefiles into a Geodatabase
2) layers created using AutoCAD
- e.g. AutoCAD .dxf, .dwg formats (often with limited success)
3) layers created using other GIS software
- e.g. MapInfo (business GIS software)
4) raster image layers in either binary or ASCII formats
- the import process is accomplished using the Catalog window in ArcMap or tools from
ArcToolbox
Table Joins - ANS-- once shapefiles or feature classes are added to ArcMap
- we can append or access additional attribute information (tabular data) with joins and
relates
1) Joins (a 'table join" appends data from a table to the attribute table)
a) one-to-one relationship
- attribute information is added to features by joining data from a table with same
number of records
- the tables appear joined in ArcMap but remain separate on disk
- e.g. we can join a U.S. county census table to U.S. county polygonsb) many-to-one
relationship
- attribute information from one record is joined (appears duplicated) to multiple records
- the tables appear joined in ArcMap but remain separate on disk
, - e.g. we can join data from a U.S. states table to multiple county polygons
- The table with fewer records is joined to the attribute table with many records.
- The data from the table with fewer records appears to be duplicated to match the
records in the attribute table.
Table Relates - ANS-2) Relates (a "table relate" provides access to tabular data that is
related to features)
- attribute information associated with a feature can be accessed (but not directly joined)
- the tables remain separate in ArcMap and remain separate on disk
- the 'related' records are accessed when records in one table are selected
c) one-to-many relationship
- e.g. list of tenants living at a single address
Tabular Data Formats - ANS--most commonly, we bring tabular data into ArcMap in a
dBase IV (.dbf) or Excel format
-dBase IV is the native format for shapefile attribute tables (the .dbf part of a shapefile)
Creating Your Own Data - ANS--in many cases the data we are interested in simply
does not exist and we have to create our own data
-the three most common methods of creating data are:
-digitizing - heads-up digitizing of scanned maps or digital imagery
-digital image processing - requires the use of remote sensing software
-mobile field mapping - most commonly involves the use of GPS
Digitizing - ANS-- most GIS data are created by digitizing either scanned paper maps or
digital remote sensing imagery
- in older times, paper maps were digitized directly on a digitizing table using a digitizing
puck
- today, we use heads-up digitizing - the process of tracing features on the computer
screen using the mouse
- to digitize features, the process is fairly straight forward:
- open ArcCatalog and create a new empty shapefile or feature class in a geodatabase
- the new shapefile or feature class can be a point, line or polygon layer
- the layer must be assigned a coordinate system (either geographic or projected)
- the assigned coordinate system must match the coordinate system of the image layer
- open ArcMap and add the image layer (either a georeferenced scanned map or digital
imagery)
- add the new empty shapefile or feature class to the Table of Contents
- use the Editor toolbar and Start Editing to begin an edit session
- select a template and a tool and use mouse clicks to trace the feature of interest -
double click to finish
- the new feature is created - then select Save Edits (good practice)
- we can now add attribute information to the records in the attribute table
- repeat the process for each feature
- finally, select Stop Editing and Save Edits
Solutions
Geoprocessing - ANS-G tools are commonly used tools that we normally use to prepare
data for further analysis.
Buffer - ANS-creates polygon buffers around point, line, or polygon features using a
specified distance. Used to select features in other layers. Ask a spatial question of
what features are within a certain distance of other features. Proximity analysis. Ex:
What pipelines are within 100 ft of oil wells.
Clip - ANS-features (either points, lines, or polygons) in one layer using the extent of a
polygon in another layer. Important toll to help simplify data. Helps extract only the
features needed within a study area to create a smaller, more manageable dataset.
Used this tool to clip the MergedContours layer using the StudyArea layer in the
Caprock Canyons Project
Dissolve - ANS-Used to aggregate (combine) features in a single layer based on
common attribute values. Works on polygons and line features.
Intersect - ANS-Calculates a set of new polygons based on the combination of two or
more layers. The new output layer contains all of the features present only in the
overlap of the input layers. The input features can be point, line, or polygon, but the
output will contain features with the lowest dimension (ex. intersect lines and polygons
will output lines)
Union - ANS-Calculates a set of new polygons based on the combination of two or more
layers. The new output layer contains all of the polygons present in the overlap of the
input layers, plus the polygons that exist where there is no overlap. Answers the most
basic question in geography: What is on top of what? Ex. What vegetation is on top of
what type of soils? So you can get an idea of vegetation productivity with different soil
types.
Merge - ANS-Used to combine 2 or more layers that do not overlap into one layer. Used
to combine either 2 or more point layers, 2 or more line layers, or 2 or more polygon
layers. Note that we used this tool to merge the 2 contour (hypsography) layers in the
Caprock project.
Select by Location - ANS-Selects feature in one layer based on a spatial relationship to
features in another layer. There can be several different types of spatial relationships
,between layers. These relationships include selecting features that are completely
within, or selecting features that intersect, as well as other types of spatial relationship.
Spatial Analysis in GIS - ANS-The 2 volume ESRI Guide to GIS Analysis describes 11
basic types of spatial analysis that can be accomplished with a GIS. The following are
ex. of each of these Spatial Analysis capabilities. Can be used to do 11 different things.
Basic Measurement - ANS-Can use the basic Measure tool or the Point Distance tool in
the ArcToolbox. a.) distance: distance between point features, distance between line
features, distance between polygon features, or any combination of the above. b.)
length: dist. along a line feature -Calculate the distance along a road, pipeline or stream
segments, perimeter of a polygon - calculate the length of fenced needed to enclose a
pasture c.) area: area of a polygon or multiple polygons-calculate the total area of a
lake, or land use types in a city, county or state. NOTE: If you import a shape file to a
geodatabase, ArcGIS automatically calculates a length and area field: for a line layer,
the length-field value is the length of each line feature, for a polygon layer, the area-field
value is the area and the length-field value is the perimeter, the values calculated in
these length and area fields are based upon the units of the projection, if the layer is
unprojected, the length and area values are decimal degrees (which is meaningless), if
the layer is projected, the length values will be in meters or ft and area values in m
squared or feet squared.
Import Data - ANS-- we can also import data into ArcGIS (using tools in ArcToolbox)
- import implies that we have to go through a file conversion process
- since Geodatabases store GIS data very efficiently we can import:
1) shapefiles into a Geodatabase
2) layers created using AutoCAD
- e.g. AutoCAD .dxf, .dwg formats (often with limited success)
3) layers created using other GIS software
- e.g. MapInfo (business GIS software)
4) raster image layers in either binary or ASCII formats
- the import process is accomplished using the Catalog window in ArcMap or tools from
ArcToolbox
Table Joins - ANS-- once shapefiles or feature classes are added to ArcMap
- we can append or access additional attribute information (tabular data) with joins and
relates
1) Joins (a 'table join" appends data from a table to the attribute table)
a) one-to-one relationship
- attribute information is added to features by joining data from a table with same
number of records
- the tables appear joined in ArcMap but remain separate on disk
- e.g. we can join a U.S. county census table to U.S. county polygonsb) many-to-one
relationship
- attribute information from one record is joined (appears duplicated) to multiple records
- the tables appear joined in ArcMap but remain separate on disk
, - e.g. we can join data from a U.S. states table to multiple county polygons
- The table with fewer records is joined to the attribute table with many records.
- The data from the table with fewer records appears to be duplicated to match the
records in the attribute table.
Table Relates - ANS-2) Relates (a "table relate" provides access to tabular data that is
related to features)
- attribute information associated with a feature can be accessed (but not directly joined)
- the tables remain separate in ArcMap and remain separate on disk
- the 'related' records are accessed when records in one table are selected
c) one-to-many relationship
- e.g. list of tenants living at a single address
Tabular Data Formats - ANS--most commonly, we bring tabular data into ArcMap in a
dBase IV (.dbf) or Excel format
-dBase IV is the native format for shapefile attribute tables (the .dbf part of a shapefile)
Creating Your Own Data - ANS--in many cases the data we are interested in simply
does not exist and we have to create our own data
-the three most common methods of creating data are:
-digitizing - heads-up digitizing of scanned maps or digital imagery
-digital image processing - requires the use of remote sensing software
-mobile field mapping - most commonly involves the use of GPS
Digitizing - ANS-- most GIS data are created by digitizing either scanned paper maps or
digital remote sensing imagery
- in older times, paper maps were digitized directly on a digitizing table using a digitizing
puck
- today, we use heads-up digitizing - the process of tracing features on the computer
screen using the mouse
- to digitize features, the process is fairly straight forward:
- open ArcCatalog and create a new empty shapefile or feature class in a geodatabase
- the new shapefile or feature class can be a point, line or polygon layer
- the layer must be assigned a coordinate system (either geographic or projected)
- the assigned coordinate system must match the coordinate system of the image layer
- open ArcMap and add the image layer (either a georeferenced scanned map or digital
imagery)
- add the new empty shapefile or feature class to the Table of Contents
- use the Editor toolbar and Start Editing to begin an edit session
- select a template and a tool and use mouse clicks to trace the feature of interest -
double click to finish
- the new feature is created - then select Save Edits (good practice)
- we can now add attribute information to the records in the attribute table
- repeat the process for each feature
- finally, select Stop Editing and Save Edits
