What is the Compass Rose program?

A Compass Rose is a figure that shows the principal directions (N, S, E and W). Such figures could be drawn on a floor, mounted on a stand at a cross-road, etc.

The Compass Rose program draws a conventional set of directions. In addition, however, you can specify your location along with the names of 10 more locations on the Earth. The program will then calculate the bearing and distance to each of these places and draw scaled arrows on the rose to show them.

How do we use the program?

Before you use the program, you need to make a list of locations, along with their latitude and longitude.

Please note the following:

Latitudes and longitudes are in decimal degrees, not degrees, minutes and seconds.
Latitudes in the Northern Hemisphere would be positive, those in the Southern Hemispher would be negative.
Longitudes East of the Prime Meridian would be positive and those West of the Prime Meridian would be negative.
Two decimal place accuracy is more than adequate in both latitudes and longitudes.

Here are some examples for your reference:

New York: 40.71, -74.00
Brasilia: -15.80, -47.89
Moscow: 66.76, 37.62
Sydney: -33.87, 151.21

Your list should include your own location details and up to 10 other locations.

There are two ways to use the data: Manual and Quick

Manual Entry

Enter the data manually in the various fields. Your own location goes in the top 3 fields, while the other locations are entered in the table below.
Click on the Plot It! button to see the Compass Rose.
You will find that the "Paste Values Here:" text area has some data in it. You can copy the data and use it for Quick entry mode later. This is useful if you wish to modify some of the data (e.g. locations) but do not want to enter the data manually again.

Quick Entry

Use a simple text editor to make a string containing your data.
The string should consist of , ",", ,",",, ",", , ",", , ",", , ",", , ",", , ",", , ",", ...
Each data item (location/latitude/longitude) is seprated from the next with a comma.
Here's an example of a suitable string:
Ahmedabad, 23.02, 72.57, New York, 40.71, -74.00, London, 51.51, -0.13, Moscow, 66.76, 37.62, Tokyo, 35.66, 139.65, Sydney, -33.87, 151.21, Hong Kong, 22.32, 114.17, Johannesburg, -26.20, 28.05, Brasilia, -15.80, -47.89, Nairobi, -1.29, 36.82, San Francisco, 37.77, -122.41
Copy the string and paste it in the text area marked as "Paste Values Here:" and click on the Fill button. You will find that the tables will be filled with your data.
If you wish you can edit the data in the table.
Once you are through, click on Plot It! to see the Compass Rose.
In case you have made changes to the values in the table, a new string will be available in the text area. You can copy this and use it later.

You can now right click on the image and save it as a PNG file. The image can then be converted to other formats, included in documents or printed.

True vs Rhumb bearings and distances

The page shows you a plot using either true or rhumb bearings and distances. What is the difference?

The earth is a sphere and the shortest distance between two points is along an arc of a great circle: a circle that divides the earth into two equal parts or hemispheres. Lines of longitude are great circles, as is the equator; other lines of latitude are not. The true distance between two points is that measured along a great circle and is the shortest distance between the two points. The true bearing refers to the direction in which you start moving to reach your target; however, as you move along the great circle, the bearing keeps changing!
Because the true bearing keeps changing, it is often easier to use another bearing, called the Rhumb bearing. This is got by drawing a curve (called a loxodrome) between the two points in such a way that the bearing is a constant (the curve makes the same angle with every line of latitude and every line of longitude). The distance along a loxodrome is more than the true distance, but the convenience of the loxodrome is that you keep moving in the same compass direction till you reach the other end! Loxodromes were popular with sailors, who could continue to sail on the same bearing; hence the popularity of the Mercator projection, as loxodromes on such maps are straight lines!

Better quality Compass Rose

As you may have noticed, the Compass Rose is a bitmap and hence cannot be enlarged. A vector drawing can be provided on request and on payment of a fee of USD $40 or equivalent (Rs. 3,000 INR). Please contact me at [email protected] for further details.

Why do we need a Compass Rose?

A Compass Rose, especially the one that is being provided here, has various pedagogical applications.

Awareness of the cardinal directions and relation to sunrise and sunset.
Bearings are taught as part of the curriculum in many syllabi and the Compass Rose shows the bearings of the selected locations.
The locations can be changed according to themes being discussed in school. After a summer break, for example, students can be asked where they went for holidays and the locations can be plotted. Similarly, if particular locations are being discussed in geography or history, the locations can be displayed on the rose.
The distances to the selected locations are also displayed. This can be used in a classroom to generate discussions on time taken to travel, the "meaning" of large distances, etc.
Classroom discussions can also take place about the locations: the culture, food, important landmarks, etc.