Co-Ordinate Systems And Projections In Arcmap - Engineering Assignment Help

Assignment Task

Co-Ordinate Systems  and Projections in ArcMap

For the first part of this tutorial, you will be working with a country map (cntry08.shp) of the world which originates with ESRI.

Start ArcMAP and create a new empty map. 

Add the “cntry08.shp” world map from MyAberdeen folder.

Right-click on the name of the map layer within the table of contents and select “properties”. 

When you click on the “Source” tab you will seeinformation for this map layer, including coordinate and projection information.

In this case, the coordinates are latitude and longitude (geographic coordinates) based onGCS_WGS_1984 (Geographic Coordinate System using the WGS_1984 datum). 

There is NO projected coordinate system information, becausethis particular shape file is not“projected.”

Examining coordinate systems using ArcCatalog 

The ArcCatalog window allows you quickly explore map characteristics, add maps, or rename maps. 

The ArcCatalog window can be opened by selecting Catalog, under the ‘windows’ pull down menu. It may also appear to the RHS of your View. This window unfolds /slides from the right sideof the GUI.

Using the right side of window, navigate to andright-click on the cntry08.shp and select properties

The X/Y Coordinate System Tab describes the spatial reference information (co-ordinates) – if that information has been placed in the metadata. Note:  that some maps do not have a metadatafile. 

Also note that you can see the fieldnames and some properties of the table under the“Fields” tab.

Adding a geographic grid or graticule to the map layout

Move back to the ArcMapview (you may close Catalog if you want or it will ‘fold up’) where you should still have the country map layer in the view. 

Right-click in the map window (which is also called the data frame) and select Data Frame Properties.

Select the Grids tab and click the New Grid button, and work through the defaultoptions to put a graticule in the layout window. 

Note: you will not see the grid in the data view. 

Switch to the layout view to see the latitude and longitude lines. 

Remember – thegraticule will only appear in the layout window!!

Create a quick world map as an example.

Select File on the main GUI select page and print setup and change your layout from portrait to landscape. 

Adjust your dataframe (shown as a dashed line with side “handles”) to fit the new shape of your page layout.

Note: The handles can be used to change the actual shape of the dataframe to fit the page.

Instead of Printing the Map to Hardcopy paper, select ‘export map’ in the file menu on the main GUI. This feature enables you to make an image of your map (similar to taking a picture of it). 

Change the file type to “jpeg” and make sure you save the file into your own workspace e.g. H:\drive, or as a temporary location the S:\ drive.

When you select OK the image will be rendered or drawn. You then should be able to open it up and view it - like you would any picture, or image, file-  in a graphics package. Do this to make sure everything worked. You can use IrfanView (a free graphics package) or similar which is found in one of the Utilities folders.

Note: this is also considered the best way to move graphics from ArcMap into the office suite of products
(Word or Powerpoint) e.g. when putting maps into Word files as illustrations.

Three main (re)projection operations

How do you (re)project a map layer? 

There are three possibilities:

• To change the way a map layer is displayed in the data frame without permanently changing its original projection (i.e modifying the data). Such a map layer has a defined projection and it is simply a case of reprojecting it temporarily.

• To define a projection for a map layer that has no original projection information.

• To create a new map layer with its projection permanently altered. 

1) Changing the map projection in the data frame (temporarily)

Note – the first approach only changes the way the map is viewed. Its native coordinates are not changed. The second and third techniques create a new map with new native coordinates.

Return  to the ArcMap data frame, right-click in the map window, and select Data FrameProperties. 

This time, select the Co-ordinate System tab.  Note that the “Coordinate system” tab shows only“GCS_WGS_1984” which is a geographic coordinate system, WITHOUTany projectedcoordinate system. This is because the current map on the screen is actually not projectedbased on any conventional projected coordinate system.

Click the Predefinedfolder ->Projected Coordinate Systems folder. 

Continue working your way through to the World folder (Note: plain world, not ‘Sphere-based’). A list of common projections for the world will be given. 

The term “Predefined” refers to various coordinate systems that have been pre-programmed into ArcMap.

Select the Mercator (world) projection, Apply, OK -  andexamine the pattern of latitude and longitude lines in the layout. Note the increasing area distortion in the polar regions. Note: you may need to  click the full extent button (the one that looks like a globe on the main toolbar).

Note the projection parameters for the Mercator projection. How do they differ from theWGS_1984 GCS specifications your previously viewed? Remember, all projections have bothprojection parameters (such as standard lines) as well as GCS specifications (such as spheroidand datum). In other words, projected coordinates are produced from the GCS following theconventions of the projection. 

ALSO - Modifying projection characteristics

The default settings for the Mercator projection uses 0° longitude as the central meridian (centre of the map). Change this value to -75 (75ºW), which is closer to NY (New York).

Remember that western longitudes and southern latitudes are identified by negative numbers inArcGIS. 

To change the value of the central meridian you must first make sure you are in the dataframe view (not the layout) and again right-click on the map. 

Select the Data Frame Properties andclick on the Coordinate System tab. The map should still be set on a default World-Mercator.

Click the Modify button to make the appropriate projection adjustment for changing the central meridian.Apply, OK.  And Apply, OK.   Note how changing this value changes how the data is displayed.

Remember that the cntry08.shp map itself is still in its native GCS_WGS_1984 coordinates. To seethis, right-click on the name of the map within the table of content, select “properties” and click onthe “Source” tab. The Data source box still shows only GCS_WGS_1984(no mention of Mercator projection). This confirms that the use of the Data Frame properties hasallowed us to temporarily reproject it in Mercator coordinates. 

This world map can now be closed. 

In preparation for the next stage of the Tutorial, select File, New and start a new blank map. There is no need to save the changes to Untitled.

2)    Defining (adding) projection information to an existing map that has no information

Occasionally you may find yourself with a GIS map layer that does not have its native coordinatesystem defined. 

For example the Hydrology layer (hydrology.shp) (in MyAberdeen)

Open a new empty map document in ArcMap and add the hydrology.shplayer

Examine the Properties of the layer. What does it tell you?

Now examine the Properties of the Data Frame.... What does it tell you?

Now Add the layer:  adkParkPoly.shp (a park boundary file)

Youwill get a warning message. Strictly you should not ignore this  warning and you will always need to figure out the co-ordinate system and define it as such.

However, click on Close for the timebeing. What happens? And Why?

Now examine the Properties of the adkParkPoly.shp layer.... and the Dataframe properties.

What does this tell you?

What is the difference between the two layers?

Now reverse the order in which you open these two files (hydrology and adkParkPoly). Once again IGNORE THE WARNING.What is the difference between the first order of opening the files and the second order of opening the files?

What you are witnessing in both cases is the fact that ArcGIS can project – so that the layers ‘fit’ each other - ON THE FLY! The properties of the original data files are not changed – only the view properties.This is OK for viewing but it may limit what else you can do later without addressing the Warming Message.

In the “old days” of GIS, if you attempted to overlay maps with different coordinatesystems or datums  they would not line up. 

ArcMap setsthe display coordinates based on the first map you open and then reprojectsthe second to match the first. This is called “projecting on the fly” and is a convenientfeature of ArcMAP. 

However, be warned that you should understand the coordinate system and units of every map you work with and not assume that ArcMap will take care of projection issues!!!!

3) Permanently changing projection systems

ArcGIS also provides some tools that allow you to permanently define projection information for anundefined map layer. This task is performed using ArcToolbox.

In ArcMap, click on GeoProcessing, ArcToolbox.

Within the list of tools in this menu, openData Management Tools -> Projections and Transformations.

Click onDefine Projection. 

You must identify the input map (e.g. hydrology.shp) and the coordinate system thatyou are intending to define. 

To do this, click the buttons to the right of each input field and work through the options. 

Note that you can use this tool for a map layer in your present table of contents, or you could navigate to a map layer in a folder and define its projection as well. 

When you click the button next to the coordinate system field, you click-on the Select button and navigate to your desired projection in the list, or if you already have a layer already available to be used as a reference use theImport button.

Click OK followed by another OK to finish the process. 

Opening the projected file will reveal that it has now been projected.

You have now projected the original file – which means that the original file has been replaced.

Another way to deal with projecting a file is as follows – which is very similar to above.

To do this – having already altered hydrology.shp above, you may want to download a fresh copy of hydrology.shp from MyAberdeen and save it with a different filename e.g. hydrology1.shp.

Within ArcToolbox:

selectData Management tools -> Projections and Transformations.

Click onFeature, Project

You must identify the input map e.g. hydrology.shp and the projection system thatyou intending to define e.g. the  one for the other layer you have used here.

To do this, click the buttons to the right of each input field and workthrough the options.  For the Output Coordinate System you can once again Importthe  Spatial Reference Properties of the already projected layer e.g. adkParkPoly.shp.

Click OK to select the projection and another OK to finish the process. 

It takes a few minutes to process the data transformation, and then the projected hydrology file (complete with a new filename) will be added to the view. This route means that the original file without a projection is retained and a new projected file created.

Check that the Properties of the projected hydrology file are different to those of the original hydrology file.

 

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