The reason we are turning our attention to Column 1 is that the exact positions of the marshalling yard and the passenger terminal, not to mention the exact dimensions of the canal lock, are dictated by the position of this column. Why is this true?
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For example, suppose you assemble a circle of sectional track, and then try to flatten the circle into an oval by squeezing it from opposite points. The circle of track will resist your attempt at shape-changing ("deformation"), because sectional track is built to resist deformation. To take a simple case, If you try to bend a length of straight sectional track into a curve, you will find that the rigid plastic base under the rails will not bend. The plastic will break, but it will not bend.
Everything we have said so far about resistance to deformation applies only to closed loops, such as circles or ovals. For example, suppose we gather sixteen sections of Hornby curved sectional track and begin to connect them into a circle. Suppose further that we pause before making the final connection between the last sections. We observe that the last two sections will not automatically "snap together" to complete the circle. The sixteen curved sections possess sufficient flexibility at their joints to permit the circle to remain open an inch or two, until we make the final connection.
Keep in mind that our layout contains only one closed loop - the upper-level oval. The entire remainder of the layout "hangs" from a single right-hand point at the upper level. In other words, the entire layout outside of the upper-level loop is a "long spur track with many branches". The curved track in the middle of the accompanying picture is part of this "long spur track" that "hangs" from the upper level. It is possible to change the shape of the curve you see in the picture by not making tight fits at the joints. As the following plates will reveal, this is where we can run into trouble with Column 1 if we are not careful.
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