Exercise 3
CORSE 2007
Advanced Track
Referencing Data to Real World Locations
This exercise uses Module 3 of the ESRI course “Learning ArcGIS Desktop” Create a
folder within your named folder called Projections and load the data for the You have
already accessed and downloaded the course so all you have to do is download the
Reference.exe file into the Projections folder and put the data into a folder called
Reference
There are very important concepts in this Module. There is a problem, however, and that
is that ESRI uses slightly different terms for the various projections, coordinate systems,
and datums. The introductory textural material states that:
“There are two types of coordinate systems: geographic and projected. A geographic
coordinate system is used to locate objects on the curved surface of the earth. A projected
coordinate system is used to locate objects on a flat surface—a paper map or a digital GIS
map displayed on a flat computer screen.”
Most GIS people consider coordinate systems to be State Plane or UTM and other
methods of converting geographic coordinates of the globe as Projections. Thus
discussions may be confusing at times.
As before the textural material herein is provided for reference and need not be read at
this time, The important concepts and practices were covered in the PowerPoint for this
topic.
Understanding coordinate systems
There are two types of coordinate systems: geographic and projected. A geographic
coordinate system is used to locate objects on the curved surface of the earth. A projected
coordinate system is used to locate objects on a flat surface—a paper map or a digital GIS
map displayed on a flat computer screen.
Each of these coordinate systems attempts to model the earth and feature locations
accurately, but, as you will learn, no system is completely accurate. In this topic, you will
learn the basics of how geographic and projected coordinate systems work.
Geographic coordinate systems
A geographic coordinate system is a reference system for identifying locations and
measuring features on the curved surface of the earth. It consists of a network of
intersecting lines called a graticule. The intersecting lines of the graticule are probably
familiar terms to you—longitude and latitude.
Exercise #
CORSE 2007
Advanced Track
The graticule is made up of
vertical lines, called lines of
longitude, and horizontal lines,
called lines of latitude.
Because the earth is spherical,
these lines form circles.
In a geographic coordinate system, measurements are expressed in degrees, minutes, and
seconds. A degree is 1/360th of a circle. Each degree can be divided into 60 minutes, and
each minute can be divided into 60 seconds.
Lines of longitude are called meridians. Measures of longitude begin at the prime
meridian (which defines the zero value for longitude) and range from 0° to 180° going
east and from 0° to -180° going west.
Lines of latitude are called parallels. Measures of latitude begin at the equator and range
from 0° to 90° from the equator to the north pole and from 0° to -90° from the equator to
the south pole.
The prime meridian (green line) is
the starting point for longitude
and has a value of 0. The equator
(red line) is the starting point for
latitude and has a value of 0. It
runs midway between the north
and south poles, dividing the earth
into northern and southern
D:\687321961.doc
2/6/2016
Page 2 of 1
Exercise #
CORSE 2007
Advanced Track
hemispheres.
More about prime meridians
Longitude and latitude are actually angles measured from the earth's center to a point on
the earth's surface. For example, consider the location referenced by the following
coordinates:
Longitude: 60 degrees East (60° 00' 00")
Latitude: 55 degrees, 30 minutes North (55° 30' 00")
The longitude coordinate refers to the angle formed by two lines, one at the prime
meridian and the other extending east along the equator. The latitude coordinate refers to
the angle formed by two lines, one on the equator and the other extending north along the
60° meridian.
Longitude and latitude are angles measured from
the earth's center to a point on the earth's surface.
Understanding spheroids
A geographic coordinate system attempts to model the shape of the earth as accurately as
possible. Many models of the earth's shape have been made over the years, and each has
its own geographic coordinate system. All are based on degrees of latitude and longitude,
but the exact latitude-longitude values assigned to individual locations will vary.
Two shapes that are commonly used to model the earth are a sphere and a spheroid.
The shape of the earth can be
D:\687321961.doc
2/6/2016
Page 3 of 1
Exercise #
CORSE 2007
Advanced Track
approximated by a sphere or a spheroid.
Assuming that the earth is a sphere greatly simplifies mathematical calculations and
works well for small-scale maps (maps that show a large area of the earth). A sphere does
not provide enough accuracy, however, for large-scale maps (maps that show a smaller
area of the earth in more detail). For those, it is preferable to use a spheroid.
A spheroid is a more accurate model of the earth, but it's not perfect.
More about the shape of the earth
Different spheroids are currently in use, in part because newer technology has provided
more accurate measurements of the earth's shape. Some spheroids were developed to
model the entire earth, while others were developed to model specific regions more
accurately.
For example, the World Geodetic System of 1972 (WGS72) and World Geodetic System
of 1984 (WGS84) spheroids are most commonly used to represent the whole world, while
in North America, the Clarke 1866 and Geodetic Reference System of 1980 (GRS80)
spheroids are most commonly used.
Why do you need to know about spheroids? Because ignoring deviations and using the
same spheroid for all locations on the earth could lead to measurement errors of several
meters or, in extreme cases, hundreds of meters.
Understanding datums
Now you know that a geographic coordinate system uses a spheroid (or less accurately a
sphere) to model the earth. You also know that a spheroid doesn't describe the earth's
shape exactly—a perfectly smooth spheroid does not reflect the undulations and other
variations on the earth's surface. Because no single spheroid can model the bumpiness all
over the earth's surface, there is more than one spheroid in use.
A geographic coordinate system needs a way to align the spheroid being used to the
surface of the earth for the region being studied. For this purpose, a geographic
coordinate system uses a datum. A datum specifies which spheroid you are using as your
earth model and at which exact location (a single point) you are aligning that spheroid to
the earth's surface.
The red spheroid is aligned to the earth to preserve accurate
measurements for North America. The blue spheroid is aligned
to the earth to preserve accurate measurements for Europe.
A datum defines the origin of the geographic coordinate system. The origin is the point
where the spheroid matches up perfectly with the surface of the earth and where the
latitude-longitude coordinates on the spheroid are true and accurate. All other points in
D:\687321961.doc
2/6/2016
Page 4 of 1
Exercise #
CORSE 2007
Advanced Track
the system are referenced to the origin. In this way, a datum determines how your
geographic coordinate system assigns latitude-longitude values to feature locations.
Just as there are different spheroids for different parts of the world, there are different
datums to help align the spheroid to the surface of the earth in different regions.
Does changing datums affect your data?
Does changing datums affect your data?
If you change the datum of the geographic coordinate system, you should know that the
coordinate values of your data will also change. For example, consider a location in
Redlands, California, that is based on the North American Datum of 1983 (also known as
NAD 1983 or NAD83). The coordinate values of this location measured in degrees,
minutes, and seconds (DMS) are:
–117° 12' 57.75961" (longitude)
34° 01' 43.77884" (latitude)
Now consider the same point on the North American Datum of 1927 (NAD 1927 or
NAD27).
–117° 12' 54.61539" (longitude)
34° 01' 43.72995" (latitude)
The longitude value differs by about three seconds, while the latitude value differs by
about 0.05 seconds.
In both the NAD 1927 and the NAD 1983
datums, the spheroid matches the earth
closely in one part of the world (North
America) and is quite a bit off in others.
Notice that the datums use different
spheroids and different origins. For NAD
1927, the origin aligns the Clark 1866
spheroid with a point in North America.
For NAD 1983, the origin (the center of
the earth) aligns the center of the spheroid
with the center of the earth. [Click to
enlarge]
The most recently developed and widely used datum for locational measurement
worldwide is the World Geodetic System of 1984 (WGS 1984). This datum is identical to
NAD 1983 for most applications. The coordinates for the same location (Redlands,
California) using WGS 1984 are:
–117° 12' 57.75961" (longitude)
34° 01' 43.778837" (latitude)
D:\687321961.doc
2/6/2016
Page 5 of 1
Exercise #
CORSE 2007
Advanced Track
Projected coordinate systems
The surface of the earth is curved but maps are flat. To convert feature locations from the
spherical earth to a flat map, the latitude and longitude coordinates from a geographic
coordinate system must be converted, or projected, to planar coordinates.
A map projection uses mathematical formulas
to convert geographic coordinates on the
spherical globe to planar coordinates on a flat
map.
A projected coordinate system is a reference system for identifying locations and
measuring features on a flat (map) surface. It consists of lines that intersect at right
angles, forming a grid. Projected coordinate systems, which are based on Cartesian
coordinates, have an origin, an x and a y axis, and a unit for measuring distance.
Projected coordinate systems are based on Cartesian
coordinates which use a grid. Feature locations are
measured using x and y coordinate values from the point of
origin.
The origin of the projected coordinate system (0,0) commonly coincides with the center
of the map. This means that x and y coordinate values will be positive only in one
quadrant of the map (the upper right). On published maps, however, it is desirable to have
all the coordinate values be positive numbers.
To offset this problem, mapmakers add two numbers to each x and y value. The numbers
are big enough to ensure that all coordinate values, at least in the area of interest, are
positive values. The number added to the x coordinate is called a false easting. The
number added to the y coordinate is called a false northing.
D:\687321961.doc
2/6/2016
Page 6 of 1
Exercise #
CORSE 2007
Advanced Track
By adding a large number to each x and y value, all
coordinate values on the map are positive. In the graphic
above, a false easting value of 7,000,000 was added to each
x coordinate. A false northing value of 2,000,000 was
added to each y coordinate.
Working with coordinate systems in ArcGIS
All geographic datasets have a geographic coordinate system (GCS). Some datasets also
have a projected coordinate system (PCS). When you add a dataset to ArcMap™,
ArcMap detects the geographic coordinate system and the projected coordinate system if
there is one.
If all the data you want to display on a map is stored in the same geographic coordinate
system, you can just add it to the map—the layers will overlay properly. If some of the
datasets also have projected coordinate systems, even if they are different, you can also
just add them to the map without data alignment worries—ArcMap will automatically
make the layers overlay using a process called "on-the fly projection." The geographic
coordinate system is the common language. ArcMap can convert the geographic
coordinate system to any projected coordinate system and it can convert any projected
coordinate system back to the geographic coordinate system.
An issue arises when you want to display datasets that have different geographic
coordinate systems on the same map. The first layer you add to an empty data frame
determines the coordinate system for the data frame. If that layer has a projected
coordinate system, the data frame will have that same projected coordinate system. If you
add a layer that has the same geographic coordinate system but a different projected
coordinate system (or no projected coordinate system at all), ArcMap will perform an onthe-fly projection and convert the data to the data frame's projected coordinate system.
The layers will overlay properly.
If, however, you try to add a layer that has a different geographic coordinate system,
ArcMap will display a warning message telling you that it may not be able to properly
align the data. ArcMap can still project the data on the fly, but it can no longer guarantee
perfect alignment. (For perfect data alignment, you need to apply a transformation to
make the geographic coordinate systems match—transformations are beyond the scope of
this course.)
D:\687321961.doc
2/6/2016
Page 7 of 1
Exercise #
CORSE 2007
Advanced Track
How do you know what coordinate system your data is stored in? You can view the
coordinate system information for a dataset in ArcCatalog™, in its metadata. If a dataset
has no coordinate system information in its metadata (it's missing), you may not be able
to display the data in ArcMap. You may need to do some research to find out the
coordinate system, then define the coordinate system using the ArcGIS tools provided.
You will do this in the exercise coming up.
What happens when coordinate system information is missing?
When you add a dataset to ArcMap that is missing coordinate system information,
ArcMap will try to read the coordinates of the data and determine whether they have been
projected. If the coordinates are in the range of longitude-latitude values (x = ±180, y =
±90), ArcMap will add the data to the map and project it on the fly, although there may
be inaccuracies because ArcMap cannot determine the geographic coordinate system for
the data.
If the coordinates are not in the range of longitude-latitude values, ArcMap will display a
warning. It will still add the data to the map, but it cannot project it on the fly. The result
is usually that the data doesn't "fit" in the same coordinate space as the rest of the data,
and either doesn't display or has serious alignment problems. In this case, you'll have to
enter the necessary coordinate system information yourself in order to display the data
properly on a map.
Map units are the units in which the coordinates for a dataset are stored. They are
determined by the coordinate system. If the data is stored in a geographic coordinate
system, the map units are usually decimal degrees (degrees, minutes, and seconds
expressed as a decimal). If the data is stored in a projected coordinate system, the map
units are usually meters or feet. Map units can be changed only by changing the data's
coordinate system.
Display units are independent of map units—they are a property of a data frame. Display
units are the units in which ArcMap displays coordinate values and reports
measurements. You can set the display units for any data frame and change them at any
time.
More about decimal degrees
Recall that latitude and longitude coordinate values are actually angle measurements.
Angles are measured in degrees. For latitude-longitude coordinates, degrees can be
expressed two ways: as degrees, minutes, seconds (DMS) or as decimal degrees (DD). In
a GIS, decimal degrees are more efficient because they make digital storage of
coordinates easier and computations faster.
Below is an example of how to convert a coordinate location from DMS to DD.
The latitude of London expressed in DMS is 51° 29' 16" North. To convert this location
to DD, follow these steps:
1. Divide each value by the number of minutes (60) or seconds (3600) in a degree:
D:\687321961.doc
2/6/2016
Page 8 of 1
Exercise #
CORSE 2007
Advanced Track
29 minutes = 29/60 = 0.4833 degrees
16 seconds = 16/3600 = 0.0044 degrees
2. Add up the degrees to get the answer:
51° + 0.4833 ° + 0.0044 ° = 51.4877 DD
D:\687321961.doc
2/6/2016
Page 9 of 1
Exercise #
CORSE 2007
Advanced Track
Mod 3:Exercise 1:View and modify coordinate system
information
On July 27, 1866, after many attempts, the final (original) transatlantic cable was
successfully laid, connecting Europe with America. The cable spanned a distance of
1,686 nautical miles between Trinity Bay in Newfoundland and Valentia Harbor in
Ireland (Moorshead).
You're writing an article about the fascinating history of the transatlantic cable and, in it,
you want to include a map showing the location of the cable as it stretched across the
North Atlantic. You're going to create a GIS map.
You've collected some GIS data, including major latitude and longitude reference lines,
world countries, states and provinces of North America, the transatlantic cable, and a
bathymetry layer representing the depth of the ocean in meters for the North Atlantic
region.
Before you can create the map, you need to make sure the data will properly align. In this
exercise, you will first examine the coordinate system information for each dataset, then
add the data to ArcMap and observe the results. For your map, you want to choose the
best coordinate system for displaying all the data.
Estimated time to complete: 30 minutes
Before you begin
The data for this exercise is contained in the following files:


LearnArcGIS.exe (Course data file)
Reference.exe (Module data file)
If you have not downloaded one of these files, you should download the data now.
Need help? Course data instructions
Step View data in ArcCatalog
1
Start ArcCatalog.
Navigate to your VirtualCampus\LearnArcGIS folder connection. Expand the
Reference folder.
You see two folders, CoordSys and Project. The CoordSys folder contains the data
you will work with in this exercise.
VIEW RESULT
Can't find your data?
The Contents tab should be active.
D:\687321961.doc
2/6/2016
Page 10 of
Exercise #
CORSE 2007
Advanced Track
Click the CoordSys folder, then click the Thumbnails button
.
You see thumbnail graphics for all the datasets stored in this folder.
VIEW RESULT
Next, you will examine the metadata for each dataset.
Step Review metadata for each dataset
2
Expand the CoordSys folder. Click countries.shp, then click the Metadata tab.
In the Stylesheet drop-down list on the Metadata toolbar, choose FGDC.
VIEW RESULT
A summary of the metadata is shown in the green box.
To get more specific coordinate system information, scroll down and click the
Spatial Reference Information link. (The term "spatial reference" is often used
interchangeably with coordinate system.)
VIEW RESULT
What is the name of the geographic coordinate system?
Answer
Notice that the names of the datum and ellipsoid (another term for spheroid) are the
same as the name of the coordinate system. WGS_1984 is probably the most
common datum used for GIS datasets that have a global extent (world data).
In the Catalog tree, click geogrid.shp and explore its spatial reference information.
What is the coordinate system of geogrid.shp?
Answer
Click North American States.shp.
This data is stored in the Mercator coordinate system.
VIEW RESULT
What kind of coordinate system is Mercator? (Hint: View the Spatial Reference
Information.)
Answer
Notice that the underlying geographic coordinate system is GCS_WGS_1984, the
same used for the countries and geogrid datasets.
Click noratlantic.
This dataset is an ESRI grid that represents the bathymetry of the North Atlantic
Ocean—the depth of the ocean floor in meters. You will learn about the grid data
format in the next module.
Notice that the coordinate system for the noratlantic data is Equirectangular.
Scroll down and click the Spatial Reference Information link.
You see that the data has both a projected coordinate system and a geographic
coordinate system.
VIEW RESULT
Notice that both coordinate systems are user-defined. This means that each
coordinate system has been customized in some way.
Click Cable.shp.
There is no coordinate system information in the green box, and there is no Spatial
Reference Information link.
D:\687321961.doc
2/6/2016
Page 11 of
Exercise #
CORSE 2007
Advanced Track
VIEW RESULT
The coordinate system metadata is missing, but a dataset's coordinate system is also
recorded in its properties. Next, you'll check the Cable.shp properties to see if you
can find the information there.
Step View cable data properties
3
Right-click Cable.shp, then choose Properties.
In the Shapefile Properties dialog box, click the XY Coordinate System tab.
VIEW RESULT
Notice that the coordinate system is Unknown. This means that ArcGIS does not
know the coodinate system of the data. Later, you will determine the coordinate
system of the data and enter this information into the properties so ArcMap can
display the data properly.
For now, click OK to close the Shapefile Properties dialog box.
Step Add the first dataset to ArcMap
4
You are ready to create your map of the transatlantic cable. You will add the
datasets to ArcMap one at a time. Remember, the first dataset you add determines
the coordinate system of the data frame.
REVIEW CONCEPT
Click the Launch ArcMap button
. If you see a dialog box, click OK to start
using ArcMap with a new empty map.
Arrange your ArcCatalog and ArcMap windows so you can see both.
In the Catalog tree, click geogrid.shp and drag it into the ArcMap map display area.
VIEW RESULT
The major world latitude and longitude lines display.
Next, you will check the coordinate system of the data frame. Remember that the
coordinate system of the geogrid is GCS_WGS_1984.
In the table of contents, right-click Layers (the data frame name) and choose
Properties. In the Data Frame Properties dialog box, click the Coordinate System
tab.
The data frame's coordinate system is also set to GCS_WGS_1984.
VIEW RESULT
Click OK.
Next, you will change the line color of the geogrid and display its feature labels.
Right-click the line symbol. In the Color Selector, click Gray 60%.
Right-click geogrid and choose Label Features.
VIEW RESULT
Step Add a dataset with the same coordinate system
5
Now you will add the countries dataset to the map. Recall that its coordinate system
D:\687321961.doc
2/6/2016
Page 12 of
Exercise #
CORSE 2007
Advanced Track
is also GCS_WGS_1984, the same one set for the data frame.
In ArcCatalog, click countries.shp and drag it into the ArcMap map display area.
ArcMap displays the layers together without any problem.
VIEW RESULT
Next, you will change the symbol for the countries.
In the ArcMap table of contents, click the countries symbol to open the Symbol
Selector.
In the Options area, change the Fill Color to Malachite Green and change the
Outline Color to Mango.
VIEW RESULT
Click OK.
Next, you will add a dataset with a projected coordinate system.
Step Add a dataset with a projected coordinate system
6
In this step, you will add the North American States data to the map. Recall that this
layer has a projected coordinate system, World Mercator, and a geographic
coordinate system, GCS_WGS_1984.
Drag North American States.shp from ArcCatalog into ArcMap.
The North American States display in the correct location.
VIEW RESULT
ArcMap read the coordinate system information and projected it on-the-fly to match
the coordinate system of the data frame.
Next, you will change the symbol for the states.
Click the symbol for North American States. In the symbols list on the left, click
Hollow.
Change the Outline Color to Mango.
Click OK.
VIEW RESULT
Next, you will add the noratlantic dataset, which has a different coordinate system.
Step Add a dataset with a user-defined coordinate system
7
Recall that the noratlantic dataset has a user-defined projected coordinate system
and a user-defined geographic coordinate system.
Add noratlantic to ArcMap.
ArcMap displays a message about the geographic coordinate system.
VIEW RESULT
This message means that the noratlantic data has a different geographic coordinate
system than the data frame. Without a common geographic coordinate system,
ArcMap can't guarantee that the map layers will perfectly align.
ArcMap will still project the data on the fly. Sometimes the data will align closely,
other times it won't.
Click Close to close the message.
ArcMap attempts to display the noratlantic data in the correct location.
Right-click noratlantic and choose Zoom To Layer.
D:\687321961.doc
2/6/2016
Page 13 of
Exercise #
CORSE 2007
Advanced Track
VIEW RESULT
In this case, ArcMap did a good job of aligning the bathymetry data with the other
data in the map.
Next, you will change the symbology for the noratlantic data so that it looks like
water.
Right-click noratlantic and choose Properties. In the Layer Properties dialog, click
the Symbology tab.
In the Show area on the left, click Classified.
In the Classification area on the right, click Classify.
Change the Method to Defined Interval.
The ocean floor depths are measured in meters. You would like each class to
represent 1,000 meters of depth, so you will set the interval size to 1,000.
In the box next to Interval Size, type 1000.
VIEW RESULT
Press your Tab key.
The histogram below and the Break Values update to reflect the new interval.
VIEW RESULT
Click OK.
The new classification displays in the Symbology tab.
Right-click the Color Ramp down arrow and choose Graphic View.
You see the text version of the color ramp list.
From the Color Ramp drop-down list, choose Cyan-Light to Blue-Dark.
VIEW RESULT
You will flip the colors so that the deepest ocean floor will be dark blue and the
shallow ocean floor will be light cyan.
Click the Symbol field name and choose Flip Colors.
VIEW RESULT
Click OK.
The noratlantic layer displays with the new symbology.
VIEW RESULT
Next, you will add the cable data to ArcMap. Remember, this data has an unknown
coordinate system.
Step Add a dataset with an unknown coordinate system
8
Drag Cable.shp into ArcMap.
You see a warning message.
VIEW RESULT
This message means that ArcMap cannot identify the geographic coordinate system
of the cable data. Without a common geographic coordinate system, ArcMap can't
do an on-the-fly projection. ArcMap will still try to display the data.
Click OK to close the message.
The Cable layer displays in the table of contents but not on the map.
The cable actually does display but in a different coordinate space. You cannot
view it with the other layers. To correct this problem, you will need to determine
the coordinate system of the data.
D:\687321961.doc
2/6/2016
Page 14 of
Exercise #
CORSE 2007
Advanced Track
First, you will remove the Cable layer from ArcMap.
In the table of contents, right-click Cable and choose Remove.
When the coordinate system of a dataset is unknown, you can see that the data is
almost unusable. When you come across data like this, you should try to find out its
coordinate system. You may need to talk to the person you got the data from or look
for documentation on the data source, such as a CD or Web site.
Documentation that might contain coordinate system information includes metadata
files, text files, and readme files.
In this case, you know the data came from a CD. You find the CD and learn that the
data is projected into the Robinson projection.
You need to define the dataset's coordinate system so that you can display it
properly in ArcMap. You'll use ArcCatalog to define the coordinate system.
Minimize your ArcMap window.
Step Define the coordinate system of the cable data
9
You will enter the cable's coordinate system information into its shapefile
properties.
In the ArcCatalog Catalog tree, right-click Cable.shp and choose Properties.
In the Shapefile Properties dialog box, make sure the XY Coordinate System tab is
active, then click Select.
You are going to select one of the predefined coordinate systems provided with
ArcGIS.
You see two folders, one containing Geographic Coordinate Systems and one
containing Projected Coordinate Systems.
VIEW RESULT
Double-click the Projected Coordinate Systems folder.
The Robinson projection is used for world data, so you'll look for it in the World
folder.
Double-click the World folder. Scroll to the right until you see Robinson(world).prj.
Click Robinson(world).prj.
VIEW RESULT
Click Add.
In the Shapefile Properties dialog box, you now see the details of the Robinson
projected coordinate system.
VIEW RESULT
Notice that the underlying geographic coordinate system is GCS_WGS_1984, the
same as the data frame.
Click OK.
Step Update metadata and add the cable data to ArcMap
10
Recall that the metadata for the Cable.shp file did not include any information about
the coordinate system. Next, you will update the metadata to include the coordinate
system information you just added, then you will add the data to ArcMap again.
In the Catalog tree, make sure Cable.shp is selected. The Metadata tab should be
D:\687321961.doc
2/6/2016
Page 15 of
Exercise #
CORSE 2007
Advanced Track
active.
On the Metadata toolbar, click the Create/Update Metadata button
.
The metadata updates, showing the coordinate system information you added.
VIEW RESULT
Scroll down and click the Spatial Reference Information link.
The projected and geographic coordinate systems are now listed.
VIEW RESULT
Restore your ArcMap window.
Drag Cable.shp into the ArcMap map display area.
This time, the data displays in its correct location.
Close ArcCatalog.
You'll change the cable symbol so you can see the data better.
In the table of contents, click the symbol for Cable to open the Symbol Selector.
In the symbols list on the left, scroll down and click the Freeway, Under
Construction symbol.
Change the Width to 2.70 (type the number into the box).
VIEW RESULT
Click OK.
The Cable displays with the new symbol.
VIEW RESULT
Step Measure the cable
11
Now that all the data is displaying properly in ArcMap, you will set the distance
units and measure the length of the transatlantic cable. In the next exercise, you will
measure the cable in different projected coordinate systems and compare the results.
Before measuring the cable length, you'll zoom in to the cable.
Right-click Cable and choose Zoom To Layer.
Click the Measure tool
.
The Measure window opens.
In the Measure window, click the Choose Units down arrow , point to Distance,
and click Nautical Miles.
Nautical miles are used for measuring distances across the ocean.
With the Measure Line button selected, click with your mouse pointer (ruler) at
one end of the cable feature, then drag over to the opposite end of the cable and
double-click.
The measurement displays in the Measure window. Depending on where you
clicked, your measurement may be slightly different than the one shown in the
View Result graphic below.
VIEW RESULT
The actual distance between the two ends of the cable is 1,686 nautical miles. Your
measurement may be close to this number.
Close the Measure window.
D:\687321961.doc
2/6/2016
Page 16 of
Exercise #
CORSE 2007
Advanced Track
Step Exit ArcMap
12
From the File menu, choose Exit. Click No when prompted to save changes to the
map document.
In this exercise, you examined the coordinate system information for several
datasets. This information is stored as part of the metadata for each dataset, and you
can easily view it in ArcCatalog.
You added the datasets one at a time to an empty ArcMap document and observed
how ArcMap displayed them. The first layer you add to a map document
determines the coordinate system of the data frame. When the data frame has a
geographic coordinate system and a layer has a projected coordinate system,
ArcMap can perform an on-the-fly projection and display the layer properly.
One layer you worked with had a user-defined geographic and projected coordinate
system. ArcMap warned you that the alignment of this layer might be off, but it was
still able to display the layer. However, when you added a layer with missing
coordinate system information, ArcMap could not display the data in the right
location. After you defined its coordinate system, ArcMap was able to display the
data properly.
As you've seen, understanding a dataset's coordinate system is the key to displaying
features accurately on a map.
D:\687321961.doc
2/6/2016
Page 17 of
Exercise #
D:\687321961.doc
CORSE 2007
2/6/2016
Advanced Track
Page 18 of