FOR557 – 05
Exercise 3a
Projections and Datums (Version 1)
Overview
This exercise is designed to show you some of the problems you can get into with projections
and datums. The most important one is the “where did my data go” problem. THE
QUESTIONS IN THE EXERCISE ARE TO BE ANSWERED ON THE ANSWER SHEET ON
THE LAST PAGES. Space is provided within the exercise so you can jot notes for your own
use. The questions numbers are red in the electronic version but, unless you have a color printer,
will print black! The are also 13 point to make the stand out.
Assignment
1) Download Exe3_05.exe from the schedule page.
2) Unzip the package of data. The layers, for Onondaga County, are:
a) On_hydro
b) On_hydro_utm
c) On_hydro_sp
d) On_hydro_mrctr (mercator)
e) On_b_pn
f) On_c_pn
3) LOOK AT PROJECTIONS AND METADATA
a) Open ArcCatalog and browse to your workspace and look at the first 4 layers.
b) Q1: Using the metadata tab click on the spatial link and make note in the table in the
answer sheet of the projections, datums, units etc. of each of them. To find map units
click on the Details link below the Horizontal Coordinate System details. Pay
particular attention to the local or projected bounding coordinates of each and record
them in Table 1. Record degrees to 2 decimal places and other coordinate units to 0
decimal places. Fill in the rest of the table in the answer sheet.
c) Q2: With the Preview tab selected click on each of the four layers in succession and watch
how the geography changes. These views of the data are in the native projection1 of the
layer. Fill in your observations in Table 2 in the answer sheet.
4) NOW LET’S SEE WHAT ARCMAP DOES WITH THE DATA
a) Launch ArcGIS and open a new “blank document” by clicking on the correct button in the
open dialog or by using File>New2 in the menu bar.
b) Load On_an by dragging it from ArcCatalog or by using the add data tool. This is a map
of the towns in Onondaga County. Now load On_hydro. This is the “single line” river
layer for Onondaga County. You will get a warning that On-hydro has a different
coordinate system than the current map projection. Click OK. Zoom in to areas on the
edges of the data to determine that the two layers are truly coincident. (Better do it
because you can never tell when I’ll give you data that is NOT coincident!) Although the
two layers are coincident, that is, they “line up,” they do not have exactly the same spatial
descriptions as you noted above. Q3: What is the difference in spatial metadata between
them (it is one (1) word) __________________________
Native Projection is the projection, etc. of the DATA, Since ArcMap projects “on the fly” as data is added the data
may not appear the same as shown in ArcCatalog.
2
The symbol “>’ indicates a choice within the main item. This File>New indicates the New choice under the file
menu.
1
Created on 9/21/2005 8:50 AMD:\291195236.doc
Page 1 of 5
FOR557 – 05
Exercise 3a
Projections and Datums (Version 1)
c) Zoom back out to the full extent of the data. Run the mouse cursor over the map and note
the coordinates of the cursor when it is on the map.
Q4: What coordinate System do you think the layers are in now _________?
d) Open the properties of the DataFrame. Click the “Coordinate System” tab. Is the current
coordinate system of the frame what you thought it was? If not, go back and change the
answer to Q3.
5) LOOK AT THESE LAYERS IN WINDOWS EXPLORER.
a) Q5: Is there a .prj file for On_an? Yes( ) No ( ) For On_hydro? Yes( ) No ( )
b) Is there a .xml metadata file3 for
On_an.xml? ( ) yes
no ( ) for On-Hydro.xml ( ) yes
no ( )
c) Q6: Now what is the key word in the spatial definition in the metadata that would inform
you that a shapefile does not have a .prj file?___________________
d) It is an undocumented feature of ArcCatalog that if you open a layer (shapefile or
coverage) in ArcCatalog then ArcCatalog will automatically create a .xml metadata file
even if there is no .prj file! Not only that, but if you delete the .xml metadata file
ArcCatalog just creates it again. Thus the presence of an .xml does not indicate that
projection data is available for the layer.
e) Open Notepad in windows (usually under accessories) and open On_hydro.prj.. (Since it
is not a text file you will have to change File Type to “All Files”).
f) QA14: Insert a return before each item in CAPITAL letters (Like GEOGCS) so that each
of these is on a separate line. Print it and attaché it to your report.
6) BACK TO LOOKING AT DATA IN ARCMAP.
a) Add On_c_pn. You may get the “one or more layers is missing spatial reference ….”
Click OK (As if you have a choice!).
b) Q7: Zoom to the full extent. Toggle the layer on and off. Do you see On_c_pn
or anything else? Yes ( ) No ( ) (Note that the check boxes for the layers are grayed.)
c) Q8: Humm. So click “zoom to layer” for on_c_pn. Is it there? Yes( ) No ( ).
d) Q9: What are the coordinates of the mouse cursor in this on_c_pn?
_____________________. That’s pretty interesting, isn’t it. What does that tell you?
_____________________
e) Q10: was redundant question - ignore
f) Note: If you answered Yes to Q7 or No to Q8 you did something wrong!
g) Q11: And why is the display like that? (Answer on the back of the answer sheet.) . Hint:
it’s the coordinates. What’s the difference between their Northings??
h) Q12: Zoom to each of the layers again. Are they different in shape? If so, why?
7) A DIFFERENT PROBLEM
a) Click File>New and select “Blank Document”. (Only Joe Bozo would not save the current
mxd!).
b) Add on_c_pn to the blank map.
c) What is a Northing coordinate anywhere in the layer’s map? _________________
3
4
The .xml file is the metadata file. ArcMap does NOT read the .xml file. It gets spatial data from the .prj file.
Question numbers with a “A” are attachments to your report
Created on 9/21/2005 8:50 AMD:\291195236.doc
Page 2 of 5
FOR557 – 05
Exercise 3a
Projections and Datums (Version 1)
d) Add on_b_pn . What is a Northing coordinate in this layer? ____________________
e) Q13: What do you think the coordinate systems of these two layers are?
i) On_c_pn___________________
ii) On_b_pn____________________
f) Q14: Alternately zoom to the two layers. What are the differences between these layers in
addition to just the values of the coordinates? (Answer on back.)
________________________________________________________________________
________________________________________________________________________
8) GRADUATE QUESTIONS
a) Q16: Since the “on the fly” projection system is not always perfect it is best to have all
data in one coordinate system or projection. We want all the data to be in UTM Zone 18
NAD 27. Use the Define Projection Tool to create .prj files for all layers that do not have
them and the Feature>Project tool (use the search feature of the toolbox) to project the
layers with .prj files into UTM Zone 18 NAD 27. Note: You can use batch project
(maybe) and I know you can copy .prj information into aother file using import on the
project dialog.
b) Open Windows Explorer and navigate to your working directory and open it so that you
can see the files within. Click on search and select the “all files and folders” from the
“what do you want to search for” option. Add .prj to the window “all or part of the file
name” and click on search. The results should be a list of all the .prj files in your
workspace. Do a “Print Screen” and attach the results to your report.
c) As you did above print a copy of one of the .prj files you changed.
d) Q17: If you were to just change the coordinates by adding or subtracting constant values
of Northings and Eastings could you make the two versions of Onondaga County
(on_c_pn and on_b_pn) Match? (Answer on back.)
Created on 9/21/2005 8:50 AMD:\291195236.doc
Page 3 of 5
FOR557 – ‘05
Exercise 3
Datums and Projections (Version 3)
ONLY THIS AND THE REMAINING PAGES ARE TURNED IN!
Missing questions # - answer on back!
Q1: Fill in the table in the answer sheet. (1 pts each, 20 pts)
Layer
Coordinate System name
OR
Projected Coordinate
System name
Geographic coordinate units
OR
Planar Distance Units
Horizontal Datum name
& approximate extent (for degrees or units of meters
or feet, only 2 significant digits )
On_an
On_hydro
On_hydro_sp
On_hydro_utm
On_hydro_mrctr
Q2 on next page
Q3: ____________________(2)
Q4: What does it say there?___________________________________(2)
Q5: .prj - On-an Yes ( ) No ( ) (2)
.xml - On-an Yes ( ) No ( ) (2)
On_hydro Yes ( ) No ( ) (2)
On_hydro Yes ( ) No ( ) (2)
Q6: ___________________________(2)
Q7: Is On_c_pn there? Yes ( ) No ( ) (2)
Q8: Yes( ) No (
D:\291195236.doc
). (2)
5/28/2016
Page 4 of 5
FOR557 – 05
Exercise 3a
Projections and Datums (Version 1)
Q2: Observations of the shape and size of the geography of the four layers relative to that of On_an. You can use drawings or words.
(2 ea)
On_an
On_hydro
On_hydro_sp
On_hydro_utm
On_hydro_mrctr
Q9: Coordinates_______________________________________(2) ________________________________________________(4)
_____
Q10 not used
Q11: On back (6)
Q12: Layers different in shape? Yes ( ) No ( ) (2) Why? __________________________________
___________________________________________________________________________________(4)
Q13: Which coordinate system is each layer in?
i)
On_c_pn__________________(2)_
Q14: Other differences between the two layes? (4)
GRADUATE QUESTIONS
Q16: Added to exercise package. (10)
On_b_pn___________________(2)_
Total Pt UG = 66
Points off
____________
Total pts
_____________
Q17: On back (4)
What gets turned in?
Cover sheet (optional)
Answer sheets
Prj file printout(s)
Reflection page with name on back, upper right including
Name, Date, Class (357/557)
Total Pt Grad = 80
Points off
____________
Total pts
_____________
%________________________
Created on 9/21/2005 8:50 AMD:\291195236.doc
Page 5 of 5