L2 Projections

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Lesson 2: Projections

Lesson 2: Projecting Geographic Data
What you’ll Learn: Here we practice map projections and datum transformations in
ArcMap. The readings in Chapter 3, Map Projections and Coordinate Systems, of the
textbook GIS Fundamentals, provide the necessary background.

Data includes Minnesota county boundary shapefiles and a lakes dataset, both in
various projections.

What You’ll Produce: A map of Minnesota in three different statewide projections, a
map of reprojected county boundary and lakes data in central Minnesota, and a
worksheet recording areas and coordinates for various projections.

Background: The Earth's surface complexly curved. We introduce unavoidable
distortion when we flatten this curved surface onto a map, typically changing areas,
lengths, and the shapes of features. Different map projections introduce different types
of distortion, and we choose the projection which limits distortions to levels we can
accept. Different map projections represent the same point with different X and Y (or E
and N) coordinate values. We cannot mix map projections in an analysis, so we often
have to re-project some of our data layers.

Observing How Distance Changes with the Map Projection
Start ArcMap, and add two data frames. Name one Albers, and the other Mercator (see
last week’s lesson or the video Data Frames for instructions)

Activate the Alber’s Layer

Add the layers twocity_Albers.shp, and USA_48_Albers.shp.
Left click on the Measure Tool to enable it, and set the Distance Units to Miles
(see Lab 1, or video Measure Tool.mov)

Left-click once on Los Angeles, then move the mouse to New York and double left-click
on New York.

The distance between the two cites is displayed, either in a drop-down window, or at the
bottom left of the ArcMap window (it depends on the version and setup).

Your measured distance should be approximately 2,440 miles.

Activate the Mercator data frame. Add the layers twocity_Mercator.shp,
USA_48_Mercator.shp

Re-measure the distance from LA to NY. The new measurement should be

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Lesson 2: Projections
approximately 3,127 miles.

The on the “ground distance” between LA and NY is actually 2,444 miles. The
difference in measurements between the “Albers” and “Mercator” is due to unavoidable
distortion caused when we stretch measurements from the curved Earth surface to a flat
map surface.

Projecting Shapefiles
You often need to project data from one coordinate system to a different coordinate
system. We will perform
three different projections,
and produce one map
illustrating the differences ArcToolBox
between the separate Button
projections. We will also
look at the resulting
differences in the
measured area for one
feature (in our case a
Cursor
county) in each projection. coordinates

Start ArcMap, create a
new empty map, and
rename your data frame
from “Layers” to
“Minnesota Counties.”

Place the L2\minn_county.shp file in your data frame. You should see a county map of
Minnesota displayed in your screen, similar to the figure at above.

Note the location of the ArcToolbox button and the cursor coordinates. Remember,
because the toolbars are moveable, they may be in different locations than those
shown.

Move your cursor around the screen and notice the coordinate values to the lower right.
Note how these change along with the cursor position as the program displays the map
projected coordinate values corresponding to the cursor position. These data in the
minn_county shapefile are in UTM NAD83 projection. Each coordinate value is
measured in meters, so a value X = 512,349 indicates an X value of 512,349 meters to
the east of the origin.

Note that most data layers have information stored that identifies the appropriate
coordinate system. For example, the data set above is stored in the UTM, NAD83 Zone
15 coordinates. I might have another data set of the Minnesota county boundaries
which is stored in geographic coordinates (latitude/longitude), or in state plane
Minnesota South Zone coordinates, or another in an Albers coordinate system. I may

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Lesson 2: Projections
convert one data set to another through a projection. If you reproject these data layers
correctly, they will align properly.

Note that you have the option of creating a permanent reprojection or a temporary
reprojection with ArcGIS. This can be quite confusing at first, so read this section
carefully, and make sure you understand it before you go on – you will likely save
yourself much confusion and grief.

Data Frame Coordinate Systems
ArcGIS allows a data frame to have a coordinate system. Any data that is suitably
documented and is subsequently placed in a data frame is converted to that data
frame’s coordinate system “on the fly”. This means the coordinate projection is applied
to the data read from the disk, but before it is displayed. This projection is “temporary” in
that it doesn’t affect the data stored on the disk – it only reprojects the data temporarily,
for display. This allows us to display many data sets in a data frame even if the data
sets are stored in different map projections, without having to go to the trouble of
manually reprojecting each data set and saving a new version of the data set.

The “catch” comes in that when you first create a data frame, the coordinate system for
the data frame is undefined. If you do not explicitly set the coordinate system for the
data frame, it then takes the coordinate system of the first data set displayed in the
frame. All subsequent data are then displayed in this “first” coordinate system, unless
you manually override this data frame coordinate system. A few examples will clarify
this. You might also want to look at the video, Intro to Projections.

Create a New Map; (FileNew, “Blank Map”, no
need to save your existing map; OK)

Create three new data frames, using the Insert –
Data Frame operation in the main toolbar (see at
right).

Examine the Inserted three separate data frames,
note that each data frame is given a name, typically
the imaginative “New Data Frame” and
“New Data Frame 2” etc.

As described in previous Labs, you may activate a data frame by right clicking the name
in the table of contents window and selecting Activate, near the bottom of the
dropdown menu.

Select the data frame called “Layers”, which is the first one on your table of contents.

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Lesson 2: Projections
Note that you may also look at the properties of
the data frame by left clicking on the data frame
name to select it, then right clicking and
selecting Properties, from the bottom of the
drop-down menu. This will display the Data
Frame Properties window:

In Data Frame Properties there are several
tabs. The most important one for this Lab is the
Coordinate System tab. If you select it you
should see the display shown on above right.
Notice that this shows the current coordinate
system, in this case “No projection”. Notice in
the sub-window on the bottom we may select a
coordinate system.
Left click, in order, in the “Select a coordinate
system:” window, on:
 Predefined
 Geographic Coordinate Systems
 North America
 NAD 1983
 Apply
 O.K.
From now on until you change this, ArcGIS will attempt to convert any data set you
display in this frame into the NAD83 Geographic coordinate system.
Add the data layer L2\minn_county to the “Layers” data frame. Look at the data layer
minn_county. The data on the hard drive is in UTM coordinates, but these coordinates
are converted to Geographic (latitude/longitude) NAD83 before displaying. Move your
cursor about the data, and note the coordinate values in the lower right corner of the
frame – They should be different than for the UTM (meters) data you observed before,
when you first loaded the data into a data frame with an unspecified projection, which
was then adopted the UTM coordinate system.

Make one of the remaining empty data frames active (remember, select in the table of
contents, right click, and Activate). Notice the previous map disappears.

For this empty data frame, assign a coordinate system, following the same process as
above, but this time choosing an Alber’s Equal Area Conic projection, with:

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Lesson 2: Projections
Properties  Coordinate System Tab  Predefined  Projected Coordinate
Systems  Continental  North America  North America Albers Equal Area
Conic  Apply and OK.

Now, add the minn_county.shp data to this layer. Note these are projected “on the fly” to
the new coordinate system. Again, note the differences in the coordinate values for
locations in the state.

Remember, the data on hard drive (or flash drive) are still in the UTM Zone 15
coordinates. The data have just been temporarily reprojected to an Albers Equal Area
Conic projection for display.

Note that you may get a message when you display a data set that says the datums
may be incompatible, typically because there is not a datum transformation specified.
You may ignore these warnings for this exercise (ONLY!). Datum transformations are
described in the textbook, GIS Fundamentals, and elsewhere, and whether datum
transformation differences are important depend on the source and target projections,
the accuracy requirements of the data, and the goals of the analyses.

The previously described exercise shows how you may reproject the coordinate
values temporarily. This is often the case when you want to work with disparate data
sets occasionally. However, we often want to permanently project the coordinate
values in a data set from one coordinate system to another. We create a new data set,
projecting from an original source data set to a target data set.

We accomplish this in ArcGIS with the projection tool. Each time we apply the projection
tool, we identify the source data set, the output data set, and the output projection. Most
source data sets have a coordinate system associated with them, with the identity of the
coordinate system written in a file. The projection tool reads this coordinate system to
determine the input. We then specify the output, including the datum transformation, if
needed, and save the new file to a target location. Be careful to note where you save
the output file, and remember, you are not modifying the original input file; it is still intact
in its original location. If the source data set does not contain the identity of its projected
coordinate system, we must either modify it to include the coordinate system name, or
specify it during projection process.

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Lesson 2: Projections
Projecting Data to a New File – The Project Tool

Create a New Map (FILE 
NewBlank Map) and again
insert two new empty data
frames, then left click to open
ArcToolbox

Then, left click to select Data
Option: Management Tools 
Open
ArcToolbox Projections and
Select Data Transformations  Feature 
Management Project
Tools

Select (Video: Projection Tool)
Projections and The Project tool steps you
Transformations
through the process of
projecting a data layer from one
Select Project coordinate system to another.
There are several steps.

Note: If you did not create a New Map as directed above, remove any data from all data frames (right
click on data, then remove). Then for all frames, Set the projection to “No Projection” by opening the
frame properties (right click on the name in the table of contents, then properties), and left clicking Clear
in the coordinate system tab, then left clicking Apply, then OK.

Detailed instructions for specific projection examples are provided a bit further on in this
document; here we outline the general process: (read on for specific step by step instructions)
 Create a new data frame, or Activate a data frame with no projection assigned
 Start the projection tool.
 Select a starting layer (the one you wish to project; you create a new layer, the original is not
altered)
 Select a place to put the new (projected) layer.
 Select the projection parameters (they might require both projection and
geographic parameters). These parameters can be loaded from another layer
already in you new projection or you can create a new set of parameters.
 Apply the projection parameters
 If necessary, specify a geographic transformation (also called Datum
Transformations in the text book)
 Apply the projection

As a useful bit of background information, ArcGIS shapefiles store information about the
projection in a .prj file. For example, a layer named minn_county may have projection
information stored in the file minn_county.prj. The .prj file is not mandatory, however,
even though all data do have a coordinate system. Without a .prj, ArcMap is ignorant of
the projection system, so when you get the unknown projection warning, it is often
because the .prj file is missing.

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Lesson 2: Projections

Detailed Instructions
This document will step you through the projection screens. You will have to use these
steps at least six (6) more times in this Lab. In later iterations, refer back to this
sequence.

Start the Project Tool from the
ArcToolbox

Browse to the layer you
wish to project
L2\minn_county.shp

Now navigate to where
you want to store the
new (projected) file.

Name the file; you don’t
need to type in the .shp
last name.
st
For this 1 step name
the new file
minn_county_albers

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Lesson 2: Projections

Select the button
To the right of the
Output Coordinate
System entry line

This opens a
window were you
set up the new
projection
information

This opens the
Spatial
Reference
Properties Box

Now you must Select or
Import parameters for
the target projection.

Often it is easier
Importing from another
layer that has the
projection you want, but
here we’ll manually
select the projection.
st
For this 1 step push the
Select button

A browse menu
opens to allow you
to define a the
output coordinate
system

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Lesson 2: Projections

Left click Projected
Coordinate Systems then
Add

Left click Continental then
Add

Left click North America
then Add

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Lesson 2: Projections

Left click “USA Contiguous
Albers Equal Area
Conic.prj”

then Add

Left click on Apply and then
OK

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Lesson 2: Projections

At times you may need to
also select a Geographic
Transformation.
Lecture and the GIS
Fundamentals book describe
geographic (also called
Datum) transformations, and
if required, you should know
the correct one to use.
Otherwise, stop the
projection process, and find
out before you proceed.

For this part of the exercise
you do not need to specify a
geographic transformation
(but you will in a subsequent
reprojection).

Left click on Ok

This will create the new data file, projecting from the original coordinate system (a UTM
zone 15 North system) to the new, Albers coordinate system you specified.

Now add the newly projected layer to an empty data frame, if it is not already added.

Change the name of this data frame to Albers (remember, right click on the data frame
name in the table of contents, then select the Properties option, then the General tab,
then type the new name in the Name textbox).

Sometimes, the target coordinate system you want to use isn’t among those provided
by ArcToolbox. Fortunately, you can create customized coordinate systems, as we’ll
now do.

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Lesson 2: Projections
Create a Custom Projection
(Video: Custom Projection)
Create or activate a new data frame
 Start the Project Tool in ArcToolbox
 Select minn_county.shp as the layer
to reproject
 Name the new file
minn_county_custom_mercator
 Click on the Select button to choose
a predefined coordinate system for
output

On the new menu window
 Choose Select > Projected
Coordinate Systems > World >
Mercator (world), select Add, then
Apply and click OK.

Now select Modify

Insert the cursor at the central meridian
value, and change it to -93.

Select apply, OK (to close this menu), then Apply, and OK to perform the projection
and close the second menu.

This returns you to the main Project menu.

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Lesson 2: Projections

Select the geographic
transformation for
NAD_83_to_WGS_1984_1, then
select O.K.

This adds your
minn_county_custom_mercator
projected layer to the active,
empty data frame.

Change the name of this data
frame to Custom Mercator (right
click on data frame in TOC >
Properties > General Tab >
Name).

Change the names of the county data sets to more or less match those of the data
frames (e.g. “Minnesota Counties Mercator”). Remember to do this by right clicking on
the shapefile layer name in the TOC > Properties > General > Layer Name).

Add a Column and Calculate Areas in an Attribute Table
Create a new EMPTY data frame. (If you already have an empty one, Activate it)
Rename this frame to UTM NAD1983

Add L2\minn_county to this data frame.

Open the attribute table for the minn_county layer (right click on the layer and select
“Open Attribute Table,” see the Video: Calculate Areas) and notice the values under
the heading “Area”. “Area” is the size of the polygon in the map units, in our case

13
Lesson 2: Projections
square meters. Note that value for “Area” is not updated automatically when you
reproject, so you must manually calculate the areas. We’ll create a new column, and
calculate the area values and place them in this column. We want to record our values
in square kilometers.

To calculate areas, do the following four steps:

First
After opening the
table, left click on
Table Options then
Add Field

Second: Name the field, Sq_km,
select Float as the Type:
Enter 17 for Precision and 5 for
Scale, and then left click on OK

Third : Right click over the new Sq_km column to bring up a
menu,
then right click on Calculate Geometry. Finally: In the displayed window,
use the Property drop down
to select Area and the Units drop
down to select Square Kilometers

Left click on OK

Click OK to the “Outside an Edit Session” warning.

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Lesson 2: Projections
Record the area in square kilometers, to two decimal places, for St. Louis County, on
the worksheet (use the Word file included with the L2 data ). This is the largest county in
Minnesota, in the northeast part of the state. This should be reported in the table in the
column you just created. Record and compare the area for St. Louis County under the
three different projections. Two should be just a bit different, and the third quite different
from the others.

Also note the shape of the state with the different projections. Not only are the absolute
areas different for each county, but notice how the general shape of the state changes
with each projection. You’ll be producing a map with all three views on the layout (see
the example near the end of this lab). You will use a fixed scale to compare these three
maps.

 First, go to the layout view, and in File > Page Setup, change to Landscape

 Then reposition the 3 data frame boxes to be side by side and about the same size
(see example near end of lab). You may want to change the colors of the layers in
each data view for easy identification.

 On the layout view, select each data frame (one at a time), right click, select
Properties and from the Data Frame tab change to a fixed scale (see figure below).

 Make each the same scale, something near 1:14,500,000 to compare them. Note
you shouldn’t enter the commas, we just show them to avoid confusion.

Choose the same fixed scale for each
data frame and Apply, then OK.

A scale of 1:14500000 works well but
any scale that will fit the three maps on a
page is fine.

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Lesson 2: Projections
Your map should look something like the figure below. Note the relative size
differences for the respective projections.

Note: Change FilePage & Print Setup to Landscape. Data Frame outlines cannot overlap or they will
obscure adjacent data. Also Data Frame outlines can be turned off using Data Frame Properties
FrameBordersnone.

16
Lesson 2: Projections
UTM and Various State plane Coordinate Systems
Create a new map by selecting File > New in the main ArcMap Frame, and add
L2\minn_count_dd.shp data layer. This is a data layer of Minnesota county boundaries
in decimal degrees coordinates. Record the decimal degree coordinates of the
northeast corner of Ramsey County (see the map figure,
at below) in decimal degrees on the sheet at the end of this Lab.

NE corner
of Ramsey
County

Coordinates

Decimal Degrees are different than Degrees
Minutes Seconds. You may have to change your
display units (right click on the data frame name,
then left click on Properties, General tab, and
select the Decimal Degree units for Display, see at
right). Note: County Names can be displayed with the Label
Features option on the Properties of the Data Layer.

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Lesson 2: Projections

You can see the coordinates in the lower right corner of the main ArcMap window; x is
the East-West Coordinate, y the North-South Coordinate. Move the cursor over to the
northeast corner of Ramsey County, zooming in as needed, and record the corner
location. Make sure you zoom in until the coordinate changes only to the right of the
decimal point when you move it just off the corner.

Now, create three new DATA FRAMES, then use ArcToolbox to reproject the
minn_count_dd layer into each of the new data frames using one of three different
coordinate systems: UTM NAD27, Minnesota State Plane South Zone 1983 (feet), and
Minnesota State Plane Central Zone 1983( feet). Use the instructions from the
previous exercise as a guide, and the notes on the next page for specific values to
select for each projection. Add the reprojected data to each frame, and rename each
frame appropriately.

Note the coordinates for the northeast of Ramsey County in each different projection,
and record them in the document (L2\L2_Data_Sheet.doc) and submit your answers
with your .pdf Maps when you complete the lab. Note that the coordinate values for
this same point should be different in different projections. Look at the difference in
the Minnesota Central and Minnesota South State Plane coordinates for the NE corner
of Ramsey County.

Which state contains the origin (x=0, y=0) for the Minnesota South State Plane Zone?

Step-by step for reprojection to UTM NAD27 (follow the numbers on the sides)

For the UTM NAD27 projection, in the projection tool:
1) Select projected coordinates, 2) UTM, 3) NAD27, 4) Zone 15N, 5) Apply-OK, 6)
For the Geographic Transformation, select the first one in the list of options.

Below are some screens you will see as you step through these processes:
For the UTM, NAD27:

2
1

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Lesson 2: Projections

3
4

5 6

If required select the 1st
Geographic Transformation in
the options list

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Lesson 2: Projections
Project minn_count_dd.shp to the MN State Plane Central, NAD83 projection
1) Select projected coordinates, 2) State Plane, 3) NAD83 (feet), 4) Minnesota Central,
then Apply/OK (not shown) 5) Select the NAD_83_to_WGS_84_1 datum
transformation, then OK.

Remember units are Feet
1 Screen views for the projection to MN St Plane Central - 1983 (Feet)
4

5
2

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Lesson 2: Projections
Now, do a similar reprojection to the one above, with the minn_count_dd.shp as input,
however, in this case the output target should be the Minnesota State Plane South-
NAD1983 coordinate system. We won’t show the screens here.

Add each data set into a unique data frame, and make sure the data frame coordinate
system matches the shape file coordinate system, and rename the data frames to
match the data sets.

Your ArcMap project should appear similar to the figure below after you have added
your data layers to the correct data frames.

Examine and record the coordinates for the northeast corner of Ramsey County, near
the arrow in the figure.

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Lesson 2: Projections
We will do one final projection, to convert data from state plane coordinates to UTM
coordinates, and display them with data already in our target projection.

Create a new ArcMap project (File > New) and display the following two files in the
same data frame

First add L2\minn_county.shp MN Counties
Then add L2\hlakes_not_projected.shp Hugo Lakes
(Ignore the warning that hlakes_not_projected is not in the same coordinates system)

Click on the zoom to full extent button, and notice the relative location of the data
contained in the two layers.

Hlakes_not_projected contains lake boundaries data in northwestern Washington
County, near the northeast corner of Ramsey County. Note that when displayed with the
Minnesota UTM data, the lakes data appear as a very small speck of dust, well south
and east of Minnesota. The data are wrongly placed relative to each other because
there are different units, different projection shapes and origins, and so the data are
projected to a different set of coordinates. This illustrates why you need to be careful in
not mixing data with different projections.

Now remove the Hlakes_not_projected from your ArcMap data frame.

The Hlakes_sp_projected
data are in the NAD27,
Minnesota State Plane
coordinate system.
Reproject these to UTM
NAD83, Zone 15N
coordinates, and add the
new reprojected layer to the
data frame with minn_county

Rearrange/recolor the data
layers so you can see both
the county and lake
boundaries. Notice the new;
correct locations for these
lake boundaries…near the
northeast corner of Ramsey
County (please see the
figure to the right). Note:
County Names can be displayed
with the Label Features option on
the Properties of the Data Layer.

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Lesson 2: Projections
The second map should look something like this:

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Lesson 2: Projections
Name:_________________________

Area of St Louis County, Square Kilometers:

UTM zone 15:

Albers:

Custom Mercator:

Coordinates of northeast corner of Ramsey County:

Projection x-coordinate y-coordinate
Decimal degrees

UTM zone 15 (meters)

Minnesota South State
Plane
(feet)
Minnesota Central State
Plane
(feet)

In what state is the origin for the Minnesota South State Plane Zone? (Extra credit):