In the kitchen, eggs and ice don’t mix too well but in map-making they do; more specifically in preparing charts of ice coverage, commonly also known as “egg charts.”
Ice on Lakes
In areas with extended periods of cold weather, the surface of lakes tends to freeze over at such times. Then people will venture out onto the ice as if it were solid rock. For many communities in the far north the only way to bring in supplies of large and heavy items is via winter ice roads across the many frozen lakes as there are no access roads over land.
Even with ice a few feet thick, a heavy 18-wheel truck will add enough weight to depress the ice at its location when crossing a frozen-over lake. As a result, such trucks are constantly going uphill then.
The main question though is whether the ice is strong enough to support the additional local weight. Of course, that depends both on the thickness and firmness of the ice, and applies equally to a man walking or a truck driving across it.
For these and other reasons, knowledge of ice coverage and its properties at any given time can be critical. Ice “egg charts” help to provide that information in a simple manner.
Egg Charts
Egg charts provide detailed information on ice coverage, ice thickness, density, strength and current trends. Such charts have been used for decades and are provided, free of charge, by various government agencies including the U.S. National Ice Center and Environment Canada for the Great Lakes and other areas with significant seasonal ice coverage.
A recent egg chart is given below. It shows the eastern Great Lakes, including the Lakes Huron, Erie, and Ontario as well as parts of the St. Lawrence River and connecting waterways.
As you can see, at the date (Jan. 30, 2014) Lake Erie (at the bottom of the chart) is covered with ice at 9/10th or higher throughout and Lake Huron with Georgian Bay (top of chart) by well over 50{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} of its entire area. In contrast, the deep Lake Ontario (on the right) is essentially still free of ice except for its shallower near-shore areas.
While the colors in this graph indicate the major sub-areas and their ice cover are easy to read, the numerous “eggs” spread along the sides give detailed information on the exact state of the ice in each area. They provide more in-depth information on the details of ice strength and cohesion. The grey areas indicate “fast ice” that is a solid uninterrupted ice cover attached to land.
The Egg Code
The egg code is a standardized representation of the ice in various parts of the Great Lakes as well as sea-ice in the Arctic and Antarctic, though it is somewhat different for the sea-ice.