map projection using arcgis - texas a&m university · brief overview of map projection using...
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Texas A&M University
Department of Civil Engineering
Map Projection Using ArcGIS
Francisco Olivera, Ph.D., P.E.
Srikanth Koka
Lauren Walker
Aishwarya Vijaykumar
Department of Civil Engineering
Texas A&M University
December 5, 2011
Contents Brief Overview of Map Projection Using ArcGIS ............................................................................. 1
Goals of the Exercise ....................................................................................................................... 2
Computer and Data Requirements ................................................................................................. 2
Procedure ........................................................................................................................................ 2
1. Projections of the World ..................................................................................................... 2
A. View of the world in geographic coordinates (longitude and latitude) .......................... 2
B. View of the world in Robinson Projection ....................................................................... 4
C. View of the world “from space” ...................................................................................... 6
2. Projections of the United States.......................................................................................... 7
A. View of the United States in geographic coordinates ..................................................... 7
B. View of the United States in Albers Equal Area projection ............................................. 8
3. Projections of Texas............................................................................................................. 9
A. View of Texas in geographic coordinates ........................................................................ 9
B. View of Texas in Lambert Conformal Conic projection ................................................. 11
C. View of Texas in the Texas Centric Mapping System (TSMS) ........................................ 12
4. Defining the Projection ...................................................................................................... 14
5. Projecting Data Using ArcToolBox ..................................................................................... 17
Brief Overview of Map Projection Using ArcGIS
Map projection involves transforming spatial data defined on the curved surface of the earth to
the flat surface of a map. A map projection is the mathematical algorithm used for this
transformation. ArcToolBox allows the transformation of data from one map projection to
another.
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Goals of the Exercise This exercise will introduce you to the procedure for projecting GIS data in ArcGIS.
Computer and Data Requirements This exercise has been completed using ArcGIS 10. All the data needed for this exercise are
contained in the MapProj.mdb geodatabase. Download the MapProj.zip file containing the
geodatabase from the class website. Unzip it and save the files to a working directory in your
computer.
Procedure
1. Projections of the World
A. View of the world in geographic coordinates (longitude and latitude) (1) Open a new ArcMap document. Add data to your map, using the Add Data button
and browse to the MapProj.mdb geodatabase in your working directory.
(2) Double click on the geodatabase to access the feature classes inside it. Select the
cntry94 and world30 feature classes while holding down the Ctrl key, and then click
Add. Make sure that world30 is below cntry94 in the Table of Contents.
(3) To show just the outlines of the features in the world30 layer, click on the symbol for
world30 in the Table of Contents. On the left hand side of the Symbol Selector window
that opens, you can see a list of color schemes; select the one named Hollow, and
then click OK. You can now see the world map in geographic coordinates.
(4) To label the countries, right-click on the cntry94 layer and select the Label Features
option in the dropdown menu. To customize the label display, right click on the layer,
and then click on Properties/Labels. To remove the labels, unselect the Label Features
in this layer option and click OK.
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(5) To label a few selected countries, first display the Draw toolbar in ArcMap. Click on
Customize/Toolbars/Draw to add it to the map.
(6) On the Draw toolbar, click the down-arrow beside the New Text button , and
select the Label option .
(7) In the Labeling Options, choose the Placement and Label Style of your preference and
close the form. Click on the countries you want to label. Save the project as
World.mxd.
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Move the cursor around on the view and you will see a pair of numbers to the bottom right
of the ArcMap window. These numbers are the coordinates of the cursor and from the
values displayed in the bottom right part of the screen you can see that they are displayed
in the degrees minutes format in decimal degrees and are the latitude and longitude of the
cursor location.
B. View of the world in Robinson Projection
The map projections of cntry94 and world30 are geographic; however, they can be viewed
in different projection systems. A common projection system for the world is the Robinson
projection.
(1) Create a new data frame in ArcMap using Insert/Data Frame. Add the world30 and
cntry94 feature classes to this new data frame by right-clicking on New Data Frame
and selecting Add Data or from the File dropdown menu.
(2) Again, rearrange the layers and change the legend of world30 as explained in the
previous section. To view the world in Robinson projection, right click on the new data
frame and click on Properties/Coordinate System.
(3) In the Select a Coordinate System box, click on Predefined/Projected Coordinate
System/World/Robinson (World) and then click OK.
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(4) Click Yes on the warning message that appears. You will see the world in the Robinson
projection. Refresh the map by clicking on the Full Extent tool , and then save the
document.
The Robinson projection is a world map projection designed to present the whole earth with
minimum distortion at any location. If you move the cursor over this space, you should see
that the coordinates are now in meters instead of decimal degrees in the projected
coordinate system.
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C. View of the world “from space”
(1) Create a new data frame and add the world30 and cntry94 feature classes to it. Again,
rearrange the layers and change the symbol color if necessary.
(2) To view the world “from space,” change the data frame coordinate system to
Predefined/Projected Coordinate System/World/The World from the Space and
select OK. As before, a warning message appears where you should select Yes. Refresh
the map by clicking on the Full Extent tool, and then save the document.
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2. Projections of the United States
A. View of the United States in geographic coordinates
(1) Create a New Empty Map file and save it as USA.mxd.
(2) Add the states and latlong feature classes to the data frame. These data are polygons
of the states of the United States and lines forming a 5-degree grid of latitude and
longitude.
(3) Click on the Zoom In tool and zoom into the contiguous United States. If
necessary, use the Pan tool to move the map to the center of the window.
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B. View of the United States in Albers Equal Area projection
The Albers Equal Area projection has the property that the area bounded by any pair of
parallels and meridians is exactly reproduced. While the projection preserves the correct
area, it somewhat distorts the direction, distance and shape.
(1) Insert a new data frame and add states and latlong. Zoom into the the contiguous
United States.
(2) To view the United States in Albers Equal Area projection, right-click on the data frame
and click on Properties/Coordinate System. In the Select a coordinate system box,
click on Predefined/Projected Coordinate System/Continental/North
America/USA_Contiguous_Albers_Equal_Area_ Conic and click OK. Choose Yes if a
warning box appears. Save your document.
Zoom in and compare the shape of the United States in geographic coordinates and in
Albers projection. You can see that in geographic coordinates the United States appears to
be wider and flatter than it does in Albers Equal-Area Projection. This effect occurs because
as you go northward, the meridians converge toward one another while the successive
parallels remain parallel to one another. When you reach the North Pole, the meridians
converge completely.
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In Albers projection, the square boxes of latitude-longitude appear as elongated
quadrilaterals with a bottom edge longer than their top edge. In geographic coordinates, the
effect of the real convergence of the meridians is lost because the latitude and longitude
grid form a set of perpendicular lines, which is what makes the United States seem wider
and flatter in geographic coordinates.
3. Projections of Texas
A. View of Texas in geographic coordinates
(1) Create a New Empty Map file and save it as Texas.mxd.
(2) Add the counties and latlong feature classes to the data frame, and rearrange the
layers and change the symbol colors if necessary.
Since we are concerned only about Texas, it is only necessary to make the Texas counties
visible.
(3) Right click on the Counties layer and then click on Properties/Symbology. In the Show
box, click on Categories/Unique Values. In the Value Field box, select State_Name.
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(4) Click the Add Values button. Click on Complete List. Then, click on Texas, the Add to
List button, and then on OK. Uncheck the <all other values> box. Click Ok.
(5) Zoom into the Texas part using the Zoom In tool. The latitude and longitude grid
displayed is at 5-degree intervals. You can determine what latitude or longitude a
particular line represents by moving the cursor to any line and read its value on the
right corner of the tool bar.
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B. View of Texas in Lambert Conformal Conic projection
The Lambert Conformal Conic projection is a standard projection for presenting maps of
land areas whose East-West extent is large compared with their North-South extent. This
projection is “conformal” in the sense that lines of latitude and longitude, which are
perpendicular to one another on the earth’s surface, are also perpendicular to one another
in the projected domain.
(1) Insert a new data frame and add counties and latlong data. Follow previous directions
to select to view only Texas.
(2) To view Texas in Lambert Conformal Conic projection, right-click on the data frame
and click on Properties/Coordinate system. In Select Coordinate System box, click on
Predefined/Projected Coordinate System/ Continental/ North
America/USA_Contiguous_Lambert_Conformal_Conic, then OK.
If necessary, select Yes in the warning message box. After clicking the Full Extent button, it
can be seen that the meridians converge to a point. Make sure that you are only viewing
Texas counties by following the steps that were outlined previously in Part A.
After zooming in to Texas with the Zoom-In tool, a more familiar shape of Texas can be seen.
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Notice that Texas appears to be tilted to the right slightly. This occurs because the Central
Meridian of the projection used is 96ºW, which would appear as a vertical line in the display
if it were shown. Regions to the west of this meridian (most of Texas) appear tilted to the
right while those to the east of this meridian appear tilted to the left.
C. View of Texas in the Texas Centric Mapping System (TSMS)
In order to present a more pleasing map of Texas, and to minimize distortion of distance in
statewide maps, the Texas Department of Information Resources has approved two
standard projections of Texas called Texas Centric Mapping System (TSMS)
(http://www.dir.state.tx.us/tgic/committee/stnd/draft-rule-2001.pdf). One of them is
Albers Equal Area and the other Lambert Conformal Conic. Their definition is:
Projection: Albers Equal Area (or Lambert Conformal Conic)
Datum: North American Datum of 1983 (NAD83)
Ellipsoid: Geodetic Reference System of 1980 (GRS80)
Map units: meters
Central Meridian: 100°W (-100.0000)
Reference Latitude: 18° N (18.000000)
Standard Parallel 1: 27° 30' N (27.500000)
Standard Parallel 2: 35° N (35.000000)
False Easting: 1500000
False Northing: 6000000 (or 5000000 for Albers Equal Area)
This means that the standard parallels, where the cone cuts the earth's surface, are located
at about 1/6 of the distance from the top and bottom of the State, respectively, and that the
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origin of the coordinate system (at the intersection of the Central Meridian and the
Reference Latitude) is in the center of the State, to which the coordinates (x, y) = (1500000,
6000000) meters is assigned, so that the (x, y) coordinates of all locations in the State are
positive.
(1) Insert a new data frame and add counties and latlong layers as done previously.
(2) Right-click on the data frame and click on Properties/Coordinate system. In the Select
Coordinate System box, click on Custom and then on New/Projected Coordinate
System button.
(3) Enter the map projection information given above as shown below. In the Geographic
Coordinate System box, click Select and in the Browse for Coordinate System window
click on North America/North American Datum 1983.prj/Add. Then click OK button to
finish projecting the data frame.
Zoom into the Texas part using Zoom In tool. (Make sure you are only viewing Texas
counties by following the steps in Part A.)
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4. Defining the Projection
Every dataset is either in a geographic coordinate system or in a projected coordinate system.
ArcMap cannot determine what projection a dataset is in unless and until it is specified. For
shapefiles, this information is stored in a file with extension prj. Geodatabases store it as a table
within the database. Even though a dataset might have a coordinate system, the corresponding
projection information might be missing. In this case, the information has to be obtained from
the data source and the projection should be defined.
If you add a layer to a data frame and its projection information is missing, you will get the
following message:
This is not a problem for displaying data as long as ArcMap does not need to project it on-the-
fly.
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In this part of the exercise, you are going to define the projection information of the STATSGO
(State soil geographic dataset) data of Texas. This dataset contains soils information for the state
of Texas, but its spatial reference properties are not defined. So, the information has to be
obtained from the host of the data. The dataset was obtained from the United States
Department of Agriculture (USDA).
(1) Before defining the projection, open a new ArcMap document, and add quad and
STATSGO to the data frame. You will see the above-mentioned warning message and
you will observe that both the layers do not overlay upon one another. This is because
ArcMap does not know the projection details of STATSGO.
(2) Close the document because you cannot define the projection of STATSGO in
ArcCatalog if ArcMap is using it.
Listed below are the values that will be used to define the projection.
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Map_Projection:
Map_Projection_Name:
Albers_Conical_Equal_Area:
Standard_Parallel: 29.50
Standard_Parallel: 45.50
Longitude_of_Central_Meridian: -96.0
Latitude_of_Projection_Origin: 23.0
False_Easting: 0.0
False_Northing: 0.0
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: coordinate pair
Coordinate_Representation:
Abscissa_Resolution: 6.35
Ordinate_Resolution: 6.35
Planar_Distance_Units: meters
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1927
Ellipsoid_Name: Clarke 1866
Semi-major_Axis: 6378206.4
Denominator_of_Flattening_Ratio: 294.9786982
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Though projection for datasets can be defined either with ArcCatalog or ArcToolBox, we will use
ArcCatalog in this exercise.
(3) In ArcCatalog, browse down to the geodatabase, open the geodatabase, right-click on
the STATSGO feature class and then click on Properties.
(4) In the Feature Class Properties wizard that opens, click on the XY Coordinate System
tab. You can see here that the XY Coordinate System for this feature class is
‘unknown’.
(5) Click on Select…A new window titled Browse for Coordinate System opens. Double-
click on Projected Coordinate Systems/Continental/North America/ USA Contiguous
Albers Equal Area Conic. Click Add.
(6) Click Apply and then click OK.
(7) Again, open a new ArcMap document and add the Quad and STATSGO layers. This
time you should not see the warning message and you will see the layers overlay one
upon another.
(8) To clearly see the layers, make sure that the first layer is STATSGO and the second is
quad. Change the symbol color of STATSGO and make it transparent (hollow).
(9) Do this by clicking on the square below the layer name and then select Hollow in the
Symbol Selector Wizard. Your map should look similar to the image below.
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5. Projecting Data Using ArcToolBox
Data in one projection can be transformed into another projection. It is very useful for all the
data layers to be one projection when they refer to the same spatial extent.
(1) Before going onto changing the projection of STATSGO, in ArcMap start ArcToolBox by
clicking on the red toolbox icon on the toolbar.
(2) Click on Data Management Tools/Projections and Transformations: Click on
Feature/Project.
(3) Click on the folder icon located to the right of the Input Dataset or Feature Class.
Browse to the folder where MapProj.mdb is located. Double-click on the geodatabase
to see all the feature classes inside it.
(4) Select the STATSGO feature class and click on the Add button to choose the feature
class that is to be projected.
(5) Select the folder icon to the right of Output Coordinate System. In the Spatial
Reference Properties wizard, click on Select.
(6) In the Browse for Coordinate System dialog box, click on Projected Coordinate
Systems/Continental/North America/USA Contiguous Lambert Conformal Conic, click
Add, and then click Apply/OK. Click OK and the program will begin to execute the
projection.
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(7) To verify if the dataset is projected properly or not, open a new ArcMap document and
add quad and STATSGO_Lambert to its data frame. If it has been projected properly,
then they should overlap.
One more thing that should be noted is the capability of ArcMap to project data on-the-fly.
Try to see the spatial reference properties of the two layers in the map by right-clicking on
each of them and then clicking on the Properties, then on Source tab in the Layer
properties wizard.
These materials may be used for research and educational purposes only. Please credit the
authors and the Department of Civil Engineering, Texas A&M University.
All commercial rights reserved. Copyright 2011: Texas A&M University.