Finding Coordinates

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Main Page > Metadata Schema > Coordinates > Finding Coordinates

Contents

Introduction

For each map in the North Carolina Maps project, we have identified the bounding coordinates -- the farthest points to the north, south, east, and west that are depicted by the map. This information is captured in order to allow for geographic-based searching. For example, instead of entering keywords or clicking on subject terms in order to find maps, users will be able to click or draw a box on a guide map that will then retrieve records of digitized maps that cover that area. To see examples of this type of search interface, visit the Kentucky Geographic Explorer.



Google Earth

Google Earth is a dynamic application that integrates satellite imagery, Google maps, and Google search. Freely available to the general public, Google Earth may be downloaded at this site: http://earth.google.com/ Visit the product tour here: http://earth.google.com/tour/index.html

For the purposes of map cataloging, Google Earth may be helpful in a variety of tasks, from locating place names or counties to finding natural features to pinpointing bounding coordinates.



Google Maps

Latitude/longitude coordinates can be determined using the [Position Finder] plugin for Google Maps. You will need to have a Google account and be logged in in order to access the "My Maps" features in Google Maps. Once the Position Finder is installed, you can simply click anywhere on a map and the coordinates for that point will display.

Gmap.jpg

Using Google Maps to find coordinates is effective for simple state maps and older maps where it may be impossible to determine precise boundaries. Google Earth, which has more features, can be a better tool for determining bounding coordinates of more detailed maps, especially those showing a very small area.


Example Search

In the example that follows, Google Earth used in conjunction with the North Carolina Gazetteer to locate and establish bounding coordinates for a map of Bells Point Shoal in Core Sound, N.C.


Step 1: Determining the Scope

This example involves a map entitled "Bells Point Shoal in Core Sound N.C." (North Carolina Collection Cm912m U58co13). The original catalog record may be found here and the digital image with metadata may be found here. The catalog records indicates the alternative spelling of "Bell's Point" but does not specify geographic location more granularly than Core Sound.


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Step 2: Finding Distinctive Features

Zooming in on the map allows the viewer to note the two most prominent (and, fortunately, named) distinctive geographic features: "Bell's Point" and "Davis Isle." Near the title, the compass indicates that magnetic north is oriented to the lower left.


Coordinates2 copy.jpg



Step 3: Quick and Dirty Searching

Opening Google Earth, the most obvious searches are attempted: Bells Point, NC and Davis Island, NC. Not uncommon for coastal islands, neither search attempt produced useful results.

Google Earth Search: Bells Point, NC

The image below is a screenshot of the Google Earth result for "Bells Point.' Note that the map displays "View Dr, Mooresville, NC." While Google Earth is a wonderful tool, false matches may lead the searcher wildly astray if careful attention is not paid to the results.


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Google Earth Search: Davis Island, NC

Similarly, the search for "Davis Island, NC" yields ten hits inland, with seemingly no relationship to the entered search term.


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Step 4: Checking Authorized Sources

As the simple, obvious search did not return immediately useful information, turning to a vetted source for geographic place names proves to be the next best step. (A list of suggested sources may be found on the Bibliography page).

The North Carolina Gazetteer provides key information on North Carolina places and placenames:

Resource: Powell, William. The North Carolina Gazetteer. Chapel Hill: University of North Carolina Press, 1968.
"Bells Point, the s end of Bells Island, on the w side of Core Sound about 1 mi. e of Marshallberg in s Carteret County.
Formerly known as Bell Point, Bell’s Point, and Great Marsh Point." (p. 38)
"Davis Island in Core Sound at the s end of Davis Shore, e Carteret County.  Named for William Davis who settled here in 1715." (p.136)

Both geographic features are considered to be in Carteret County. The town of Marshallberg in Carteret County is a good option for a secondary search effort. Google Earth returns "Marshallberg, NC" as a town in south Carteret County. To the right of the peninsula, "Bells Point" is clearly labeled.

(In an odd quirk of Google Earth, some feature and place labels are evident upon zooming in but they are not indexed for searching. This issue is especially evident for small coastal islands, peninsulas, inlets, and other features.)

Google Earth Search: Marshallberg, NC


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Step 5: Rotating Images

If needed, Google Earth allows for easy rotation of orientation. To match the angle orientation of the original map (see the image on the right), simply grab the "N" and rotate the view so that the display matches the historic map.


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Step 6: Confirming a Match

Through visual recognition and zooming, the Google Map display can be manipulated to match the scope of the original map. Here, Davis Island and Bells Point are positioned in the Google Earth viewer to reflect the historic map. In this way, the major bounding areas are identified.


Coordinates7 copy.jpg



Step 7: Returning to North-South Orientation

Angled maps may make establishment of bounding coordinates trickier than maps with traditional orientation with north as top. For this reason, the goal is to return the Google Earth display to a traditional north-south orientation. The image below shows how the two geographic representations still correspond, even after rotation.


Coordinates8 copy.jpg



Step 8: Finding Decimal Degrees

Using the historic map as a guide, a rough estimate of the westernmost point is chosen in the Google Earth viewer. As the pointer hovers over the point, coordinates display on the bar at the bottom of the Google Earth browser. Converting degrees/minutes/seconds to decimal degrees using this converter, western longitude is estimated to be -76.506944. To view decimal degrees in Google Earth, click on the Tools button on the top of the screen, then Options. Click the radio button next to "Decimal Degrees" under "Show Lat/Long."

NOTE: Points in the Western Hemisphere convert to negative longitude in decimal degrees. Points in the Southern Hemisphere convert to negative latitude in decimal degrees.

W E
N (+,-) (+,+)
S (-,-) (-,+)

For North Carolina, most map latitudes will be in the positive 30 degree range, and most longitudes will be in the negative 70s and 80s.


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Consulting with the historic map and using the decimal degree converter, the easternmost longitude point is estimated to be at -76.448611.


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In a similar fashion, the northernmost latitude coordinate is estimated to be 34.773333 -- and is a positive integer since North Carolina is in the Northern Hemisphere.


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Finally, the southernmost latitude point is estimated to be 34.727222.

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Step 9: End Result

Subject - Geographic Core Sound (N.C.) -- Maps.
Bells Point (N.C.) -- Maps.
Bells Point Shoal (N.C.) -- Bathymetric maps.
Scope United States, North Carolina, Eastern Region, Carteret County
Places Depicted Bells Point (N.C.)
Point Shoal (N.C.)
Core Sound (N.C.)
West Longitude -76.506944
East Longitude -76.448611
North Latitude 34.773333
South Latitude 34.727222
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