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Does anybody know a way to simplify a number of contour polylines derived from a raster dataset? I need to generate a map that shows contour polylines at relatively small scale. With the contour interval at a 1 meter interval, contours converge too closely, making the output lines difficult to distinguish at that scale. The spatial resolution of the original raster is 2 meters.

I'm looking for something like the 'simplify line' tool. I know this tool exists in the 'Generalization' Toolset, but I haven't got an appropriate extension.

I'd be grateful for your suggestions!

Thanks in advance.

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Why not just increase the contour interval for the small-scale maps, as suggested in the reply offered by @Jakub? Typically, as the scale decreases, the extent of the map increases, the range of elevations increases, and the contours will become closer together on the map. Except for some special purposes (akin to creating relief shading), this is undesirable because it just obscures everything else on the map and requires thinning the contours anyway. –  whuber Nov 14 '11 at 16:07
    
When you say "derived from a raster dataset", are you generating contours based on the original raster (the raster is an elevation model), or did the original raster include contour lines and you've scanned/digitized them? –  user3461 Nov 14 '11 at 16:49
    
Thanks for the responses. Jakub - I will try the 'Aggregate' method tomorrow, hopefully it will work. Whuber - I did increase the interval of contours before but that does not make any changes to polylines appearance as the resolution of the original raster is essentially the same. Kevin - I am generating the contours from original raster image. I'll let you know about my progress! Thanks for suggestions, Magda –  Magda Nov 14 '11 at 22:17
    
The polylines will not appear different at all, Magda, but by increasing the interval you will eliminate (or at least greatly reduce) the problem of having them "converge too closely." –  whuber Nov 14 '11 at 22:34

2 Answers 2

I personally would avoid creating another dataset. If you have a 1m set already then all the data you need is already there.

What if you create a definition query on the layer to select only the 2, 5 or 10m contours? (Whichever give the clearest map). This way you are not duplicating data and can avoid clutering up the map with excess lines.

This also makes it easier to experiment with various intervals without tedious geoprocessing delays.

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Thank you for all your advices! I used the 'Aggregate' tool to reduce the resolution first and then did the contour again. This worked perfect for me! –  Magda Nov 15 '11 at 10:41

Simplifying contours may cause undesirable results such as line crossing. I would recommend to generalize the input raster to 10 or 20 metre resolution (Aggregate Tool) then run the Contour tool again with the 1m interval parameter. You might need to change the contour interval to more then 1m depending on the scale of the map.

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