See Also...101 104 ISOM Index Land forms index previous next
Every fifth contour shall be drawn with a thicker line. This is an aid to the quick assessment of height difference and the overall shape of the terrain surface. Where an index contour coincides with an area of much detail, it may be shown with a normal contour line.
Line width 0.25mm
Every fifth contour should be drawn with a thicker line. This is an aid to the quick assessment of height difference and the overall shape of the ground. Where one of these contours coincides with an area of small knolls or depressions, it may be shown with a normal contour line.
Defined as line symbol 102.0. Can be drawn with any tool but bézier mode is preferable.
See most comments and tips on 101 contours. Slope lines (tags) are not thickened on index contours.
1) Draw all your contours as line type 101, thin contours, and apply the index contours when you have decided on the set that gives the best feel.
2) Selecting the correct set of contours can be tricky, but it is worth the effort to pick the best set.
Eric Peckett suggests that you can try out different sets by defining five contour symbols (101.1 to 101.5) and give every fifth contour the same symbol number. Then a global symbol change by thickness or colour will be very clear. Try printing them out with a much thicker line (0.5) to check.
3) You can't see the join...
When you have drawn a long line and had to start again at the edge of the screen, each of the segments will be a separate object. This applies even if you had the Automatic Joining option switched on. This button only ensures that the end points of a line are placed at the same co-ordinates. It does not join the two objects together.
So a long contour is unlikely to be continuous line, even if it appears to have no breaks. This can mean that if you change a contour to a major contour, you may miss sections of the line.
There are two work arounds:
Carefully check each line, following it around on the screen at a high magnification. This is not as tedious as it sounds, it also helps you to pick up other errors. We use 8x magnification for checking (key F11) and move around quickly using the F6 (move) key. Don't forget to mark all errors that you find, use the control point symbol to mark them, and come back to them later, otherwise you will forget where you have got to with the contour checking!
There are utilities to join line together that work well. Conjoin by Don Scarrott is a particularly well thought out tool, with sensible options and a limiter to make sure that the line will not become too long and upset a PostScript device. Joinline from Martin Green can be used to join any symbol line.
It is often better to have line that are not too long, as very long lines slow down the program.
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