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Projections & Coordinate Systems

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Topics:

Introduction1.

Data Frame properties and coordinate systems2.

Coordinate System & Scale3.

Comparing Coordinate Systems in ArcGIS4.

Reproject spatial dataset from one coordinate system to another5.

1. Introduction

When representing real-world features in a GIS, you need to reference the data and describe them to the correct location on the earth's

surface. This is called georeferencing. Whether you treat the Earth as a sphere or as a spheroid, you must transform its three-dimensional

surface into a flat surface. This transformation, usually using a mathematical conversion, is referred to as a map projection

Type of projections

Map projections can be classified on what spatial attribute they preserve, most importantly shape or area

Conformal projections

Conformal projections preserve local shape. Graticule lines on the globe are perpendicular. To preserve individual angles describing spatial

relationships, a conformal projection must also present graticule lines intersecting at 90-degree angles on the map. This is accomplished by

maintaining all angles, including those between intersections of arcs. The drawback of this projection is that the area enclosed by a series of

arcs may be greatly distorted in the process. No map projection can preserve shapes of larger regions.

Equal-area projections

Equal-area projections preserve the area of displayed features. To do this, the properties of shape and angle, are distorted. In equal-area

projections, the meridians and parallels may not intersect at right angles. In some instances, especially maps of smaller regions, shapes are

not obviously distorted, and distinguishing an equal-area projection from a conformal projection may prove difficult unless measured.

Coordinate Systems:

Within or on top of the projection is a coordinate system containing the x and y location values, which incorporates the ellipsoid (shape of

the earth), datum (known base values), and units e.g. metres.

Commonly used projections and coordinate systems in BC are UTM and BC Albers.

These will be further explained in lecture this week.

The UTM system is based on a Conformal projection which preserves the angle locally. "The UTM coordinate system is commonly used in

GIS for larger scale areas within a certain UTM zone. It is formed by using a transverse cylindrical projection, i.e., the standard line runs

along a meridian of longitude. The effect is to minimize distortion in a narrow strip running pole to pole".

UTM divides the earth into pole-to-pole zones 6 degrees of longitude wide. The first zone starts at the International Date Line (180 degrees

east) and the last zone, 60, starts at 174 degrees east. Northings are determined separately for the areas north and south of the equator.

Because distortion becomes extreme at northern latitudes, UTM is not normally used above 80 degrees North or South.

The image below is a UTM projection zone grid, used in northern America and many other areas.

UNBC Geog300: Projections & Coordinate System

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A typical UTM coordinate system information:

Projected Coordinate System: NAD_1983_UTM_Zone_10N Projection: Transverse_Mercator False_Easting: 500000.00000000 False_Northing: 0.00000000 Central_Meridian: -123.00000000 Scale_Factor: 0.99960000 Latitude_Of_Origin: 0.00000000 Linear Unit: Meter

The Albers equal-area conic projection, or Albers projection, is a conic, equal area map projection that uses two standard parallels.

Although scale and shape are not preserved, distortion is minimal between the standard parallels. The Albers projection is a typical Conic

type of projection, which remains the true area.

The Albers projection is the standard projection for British Columbia. The projection is with parameters of the followings:

Central meridian: -126.0 (126:00:00 West longitude) Latitude of projection origin: 45.0 (45:00:00 North latitude) First standard parallel: 50.0 (50:00:00 North latitude) Second standard parallel: 58.5 (58:30:00 North latitude) False easting: 1000000.0 (one million metres) False northing: 0.0

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2. Data Frame properties & Coordinate Systems

In this section, we will examine a dataset in several different projections and learn about the characteristics of the individual projections.

Login to a local machine and start the terminal server.

Start ArcCatalog and make sure you have a connection to Ninkasi (N:\) and a connection to N:\labs.

Create a new folder for this lab call it projections under your N:\username\geog300 folder on Ninkasi.

Start ArcMap with a new empty map file.

Click on Add Data button , navigate to N:\labs\statscan\ and add data bc_ea96, Statistics Canada EA boundary data for BC.


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A default data frame Layers is created automatically by the system. Right click on it and choose Properties.

Click Coordinate System tab. The Coordinate System tab provides information on the current coordinate system used in the display

of the data in the Data Frame. Here you can set how you want to display data, in which coordinate system.

Notice that the data are currently displayed in GCS_Clarke_1866. If you click on the "Modify" button, you can see the rest of the

parameters associated with this coordinate system. This window tells you the Datum, the Units, and the Prime Meridian information.

GCS is not a projection, but a planar expression of the latitude and longitude coordinates of the earth. It is common for ArcView data

provided by ESRI to be in the Geographic Coordinate System.


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Different projections have variable parameters. If you were to change the projection parameters, you would do so in this window. We will

accept the default parameters for now.

Click on the Cancel button from the Coordinate System Properties window to return to the Data Frame Properties window.

Now change the projection of Layers data frame to Canada Albers Equal Area Conic

In the Select coordinate system box, choose Predefined -> Projected Coordinate Systems -> Continental -> North America ->

Canada Albers Equal Area Conic in Data Frame Properties window. Click OK. Click Yes button if the warning message popped up.

1a) Has the shape and appearance of the EA boundary changed ? If so, how?

Changing the properties of a Data Frame doesn't physically change the projection and coordinate system of the dataset. It just changes the

display of data.

Right-click on bc_ea96 layer and choose Properties. Click on Source tab. You can find data source information on the selected

dataset. That includes extents of the dataset and the true coordinate system defined.

1b) The dataset is displayed in Canada Albers Equal Area Conic projection. What is its true coordinate system defined for this

dataset?

Feel free to explore the information available in the other tabs. Once you finished, click OK.

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3. Co-ordinate System & Scale

A Coordinate System is a reference system used to measure horizontal and vertical distances on a planimetric map. It is usually defined by

a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x and y

directions.

Spatial co-ordinates are given at the lower right of the ArcMap window. In this case, the dataset is in the Canada Albers Equal Area Conic

projection system in x and y. The unit is meters.

To find out what coordinate system are used for displaying the dataset's in the data frame, right click on data frame Layers and

choose Properties. Click on the Coordinate System tab. Now the current coordinate system is Canada Albers Equal Area Conic (as

you changed in the last section)

Place your mouse cursor anywhere in the display area. The scale value appears on the standard toolbar at the top, beside the Add data


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button. Whenever you zoom in or out the scale value will change.

Change the size of your view (resize the ArcMap window) and watch how the scale changes. You can do the same by using the

View options in the menu bar, experiment with the Zoom In, Zoom Out and Full Extent options. This is because scale as a ratio is

view dependent and not static.

2) Given the appearance of the data now, do you feel that the Albers Equal Area Projection is appropriate for viewing the entire

world?

Now add two more layers bc_ea96_utm and bc_ea96_albers from N:\labs\statscan\ to ArcMap. bc_ea96_utm is in UTM projection,

while bc_ea96_albers is in BC Albers projection.

Check the area of the upper right corner polygon.

3) What is the area of the upper right corner polygon in bc_ea96_utm and bc_ea96_albers respectively? Which value gives

relatively true area of the polygon?

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4. Comparing Coordinate Systems in ArcGIS

In this part of lab, we are going to explore the differences between different projections, we will create four identical data frames so we can

look at the different projections at the same time. We will do this in Layout View. Until this point, we have been working in Data View in

ArcMap. The Data View allows you to view the data of one data frame at a time, while Layout View allows you to view multiple data frames

at the same time.

First change the coordinate system of the default Layers back to its original.

Remove bc_ea96_utm and bc_ea96_albers from the table of contents by right-clicking on the layer and choose Remove.

Right click on Layers and choose properties. Click Coordinate System. Click Layers->bcea_96 polygon->GCS Clarke 1866

Make sure you have the toolbars (in the image below) showing in the window.

Click View->Toolbars and click on the check boxes beside Main, Standard, Tools, Draw, Layout to turn these toolbars on.

From the menu bar at top, click on View->Layout View to switch from Data View to Layout View. The view now appears more like a

"page preview," showing the layout of the page. Note that there are two toolbars for navigating around the data – the Layout toolbar

and the View toolbar. The following picture shows the two sets of tools. The top one is the toolbar for Layout View and the bottom

one is for Data View.

The layout tools are used to interact with the entire layout (for example, zoom in and out on the page). The View tools are for interacting

with the data in the individual data frames.

Remember that you should use the View toolbar (the lower one) when you are in Data View and the Layout toolbar in Layout View.

Since you will be working with four data frames in this lab, you need to resize the current data frame so that the other data frames can be

fitted into one layout "page." You can resize the data frame by either selecting it and dragging it on the small handles to an appropriate size,

or you can open the data frame properties and change the width and height values in the "Size and Position" tab.

Click on the Layers data frame to select it. A box with eight small handles shows up on the selected data frame. Move your mouse

cursor over a small square at a corner and drag to resize the data frame to about 1/4 size of the page.

Move the data frame to the upper left corner of the page.

When the data frame has been resized, you can simply copy and paste it to create another three identical data frames.

Right click the data frame Layers (either in the table of contents OR in the display area) and choose COPY and then PASTE to

duplicate the data frame. You should notice that a duplicated data frame with same name is now shown in the Table of Contents.

The duplicated data frame lies on top of the original one and is selected automatically

Drag the duplicated data frame to the right of the original one to make two data frames displayed side by side in the upper half of

page.

Paste another two copies of the data frame and place them side by side in the lower half of the page.

Now you have four data frames with exactly the same view and name listed in the Table of Contents. You probably notice that one data


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frame is in bold face in the table of contents. This indicates that the data frame is the active one. We want each data frame to display the

data in different projection. So it would be better to give each data frame a meaningful name which indicates the coordinate system used for

data displaying.

Change the name of the data frames to GCS_Clarke_1866, Albers Equal Area Conic, UTM, and Lambert Conformal Conic respectively and

change the data frames to corresponding projection system.

Click on the first data frame located at the upper left in the display window to select it. Right click it and choose Properties.

Click on General tab and type in GCS_Clarke_1866 in the Name box. The name of the first data frame turns to the name you just

typed in.

Change the name for the rest of three data frames to Albers Equal Conic (upper right) , UTM (lower left), and Lambert Conformal

Conic (lower right) respectively.

Note that the changes are shown in the table of contents.

Another method for creating new data frames is to click on Insert->Data Frame and then add new layers into that data frame. Try it out.

If you would like to align your data frames to one another, use the shift key and click to select all the data frames. With the all data frames

selected, right click and use the Align and Distribute commands to align and /or resize the data frames.

Note: the name of one of the data frames is in bold type in the table of contents. This means that this is the "active" data frame. If you

were to add a new layer right now, it would be added into that data frame – regardless of which data frame was "highlighted," or was

clicked on last.

To activate a new data frame, right click on the data frame and select "Activate" in the table of contents at left.

We want each data frame to display the same dataset but in different projection system, so we can see the difference between them. The

first one is displayed in Geographic. We can leave as it is. You need to change the coordinate system of other three data frames to match

their names.

Right click on the Albers Equal Conic data frame and choose Properties

Click Coordinate System tab.

Look at the Select Coordinate System section.

Click Predefined -> Projected Coordinate Systems -> Continental -> North America -> Canada Albers Equal Area Conic

Click it and click APPLY. This will set the display projection to its original coordinate system. Click OK to close the window.

Right click on UTM data frame and choose Properties.

Click on the plus sign beside Predefined and select Predefined -> Projected Coordinate Systems -> UTM->Nad1983->Nad1983 UTM

Zone10N and click APPLY. Click OK.

Your data frame (UTM) should now display your data in a Universal Traverse Mercator projection. You may need to Zoom to the layer to

make all data fit into the display area OR use the full extent button (the global button) to fit all data into the display area.

Right click bc_ea96 in the table of contents in UTM data frame and choose Zoom to Layer.

Now you should have one data frame in GCS_Clarke_1866 , one in Albers Equal Conic and one in UTM projection.

Right click on Lambert Conformal Conic data frame and choose Properties.

Click Coordinate System tab.

Click on the plus sign beside Predefined and select Projected Coordinate Systems -> Continental -> North America -> Canada

Lambert Conformal Conic and click OK.

Right click bc_ea96 data layer under each data frame and choose Zoom to layer. Do this for each data frame to make the dataset fit

into the display area.

Now you have four data frames and each comes with a different projection system (GCS_Clarke_1866, Albers Equal Conic, World

Mercator, and World Robinson)


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4) When do you think you might want to reproject your data frame, rather than reproject your individual data layers?

Now switch to Data View. Click View->Data View from top menu bar. You can only view one data frame at a time in the Data View.. To


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view the data in a data frame, you first need to make it active.

Right click on GCS_Clarke_1866 data frame in the table of contents and choose Activate

Right click on it again and choose Zoom to Layer. Examine the scale.

Do the same things for the rest of three data frames and examine the scale in each frame.

5) What is the scale for the dataset bc_ea96 displayed in each data frame?

Save your map file to your geog300\projections folder. Give the file name projections.mxd.

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5. Reproject spatial data from one coordinate system to another

We have examined several projections and coordinate systems. In most cases, we have the data that have different projection and

coordinate system which will cause problems for GIS analysis. In order to perform GIS analysis, all spatial data must be in the same

projection. How can we reproject data from one coordinate system to another to make all spatial datasets in the same coordinate system

for later analysis? This is a very common question asked by many people.

Find the coordinate system of a dataset

In order to reproject spatial data from one coordinate system to another, we need first to find out the coordinate system defined for the

current dataset. You can find the coordinate system defined for a dataset either from ArcCatalog or ArcMap.

To find out the coordinate system in ArcCatalog, right-click on the dataset in the catalog tree choose Properties. Under the XY

Coordinate System tab, you can find out the coordinate system defined for the dataset.

Right-click contours10 under N:\labs\unbc and choose Properties. Click XY Coordinate System tab. Here you can find out the

coordinate system is NAD_1983_UTM_Zone_10N.

Now let's take look at tracks under N:\labs\unbc. The Name box have Unknown value. That means there is no coordinate system

defined. For theses datasets, if we want to reproject it to another coordinate system, we need first to define the coordinate system

and then perform the reprojection. In our case here, we know that this dataset is projected in NAD_1983_UTM_Zone_10N.

Copy the dataset tracks from N:\labs\unbc to your local folder N:\username\geog300\projections\.

Right click on the local copy of tracks to open the Properties window. Now we will define the coordinate system, in the Properties

window Under the XY Coordinate System tab. The Select button allows you to choose a predefined coordinate system, while the

Import button allows you to import a coordinate system information from an existing dataset.

Click Select button ->Projected Coordinate Systems->UTM->NAD 1983->NAD 1983 UTM Zone 10N.prj and click Add button. The

projection and coordinate system information will be showing in the Details box in the Properties window. Click OK to apply the

changes. Now you are ready for reprojection. if you need.

Reproject a dataset from one coordinate system to another with ArcTools

Now we will reproject the dataset bc_ea96_new in N:\labs\statscan to BC Albers projection and UTM Zone 10 coordinate system

respectively. Reprojecting a dataset can be done by either using Project tool in ArcToolbox or by exporting the dataset using the different

coordinate system in ArcMap.

As you are going to modify the dataset bc_ea96_new, you need first copy this dataset from N:\labs\statscan to your local folder

Under the folder N:\labs\statscan, right-click bc_ea96_new and choose COPY. Navigate to your local folder N:\username\geog300\

and right-click projection folder and choose PASTE.

Now Open a new empty map file in ArcMap by clicking File->New in ArcMap. Click Yes if prompted for Saving the changes for the

current map file.and add the dataset bc_ea96_new from N:\username\geog300\projection\ to ArcMap. Note: username here has to

be replaced with your username.

Right-click on the bc_ea96_new and open the properties window, click the Source tab to examine the coordinate system information.

This dataset has no coordinate system defined.

In this case, we need first to define the coordinate system. We have known the dataset is in Geographic (GCS_Clark 1866).

In ArcToolbox, click Data Management->Projection and Transformation->Define Projection

In the popped up window, choose bc_ea96_new for the Input Dataset. Click the button right to Coordinate System. Here you can

select or import coordinate system.

Click Select->Geographic Coordinate Systems->Spheriod-based->Clark 1866.prj, click Add button. The coordinate system

information is added. Click OK and Ok again. Now bc_ea96_new. Check the properties of this dataset again to see coordinate

system info.

Now we are ready to reproject the dataset bc_ea96_new

Turn on the ArcToolbox by clicking the toolbox button (the toolbox in red) if necessary. Here you can use Project tool to reproject a

dataset.


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Click Data Management Tools->Projections and Transformations->Feature->Project to open the tool.

Click the dropdown arrow right to Input Dataset or Feature Class and select bc_ea96_new.

Click the folder button right to Dataset or Feature Class and navigate to your lab folder N:\username\geog300\projections. Type in

bc_ea96_albers for the file name and click Save.

Click the button right to Output Coordinate System to specify the new coordinate system for the output dataset. In the Spatial

Reference Properties window, click Import button. Here we will import the coordinate system information from an existing dataset.

Navigate to N:\labs\bc_data\ and double click parks_bc_alb. The BC Albers coordinate system information is added to the current

dataset. Click OK to apply the changes.

Click OK in the Project Tool window to run the tool. Once it finished, you will have a new dataset bc_ea96_albers in your local

folder. The new dataset now has been reprojected

from Geographic to BC Albers projection. You can check the coordinate system of the new dataset in ArcCatalog.

Now give a try yourself to reproject the bc_ga96_geo to NAD 1983 UTM Zone10 projection. Give the name bc_ea96_utm10 for the

output file name.

Reproject entire BC to UTM zone 10 projection is not a good choice in this case. Why? (UTM Zone concepts)

Reproject a dataset from one coordinate system to another by exporting dataset using the coordinate system in the data frame

Another easy way to reproject a dataset is using the exporting feature in ArcMap.

We need to first specify a coordinate system to the data frame which the data layers are in. Right-click on the data frame Layers

and choose Properties.

Click Coordinate System tab, here you can specify a new coordinate system for the data frame for display purpose. You can either

use the built-in coordinate systems by clicking on Projected Coordinate Systems or by importing one from an existing dataset. We

just import one from an existing dataset.

Click Import button and navigate to N:\labs\bc_data and double click parks_bc_alb. Click OK. Now all data layers in the data frame

are displayed in BC Albers projection. Note that this is the only display, the dataset is still remained in the original coordinate system.

You can check it by opening the Source tab in the layer's properties window.

Now we can export the data using the coordinate system information of the data frame. Right-click on bc_ea96_geo and choose

Data->Export Data. Here you can specify how you want to export the data. Make sure Export is set to All Features.

Click the radio button beside The Data Frame to set the output coordinate system same to the data frame.

Click the folder button right to Output Shape file or Feature Class and navigate to your local folder N:\username\geog300\projections.

Give the name bc_ea96_export_albers for the file name and click OK.

You will be prompted if you want to add the dataset into the ArcMap. Click Yes to add the data. Check the coordinate system for the

new dataset in Properties window.

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Exit from ArcCatalog and ArcMap.

Logout terminal server and local linux machine.


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