07/06/2013

Unseen auto-generated things that can lead to error

On-the-fly projection unselected
On-the-fly projection comes back when a new layer is created
Unselecting on-the-fly projection makes for a micro scale
User has to readjust to the appropriate scale with Google Hybrid...
only then create and save the point features
Everything done properly, selecting Zoom to layer extent is OK 
Going back to the newly created layer still shows correct alignment
Unseen auto-generated things that can lead to error

If a layer is created without a user really understanding what is happening behind the scene, this can lead to error which the user then blames the software (as usual) and never himself. This is why is it important for the user to understand what he is actually doing in GIS and not just follow blindly. My example is the creation of a layer using Google Hybrid as a reference base. Although a user may have started off by unselecting on-the-fly projection, the moment a layer was created, on-the-fly projection   automatically comes on again and if not unselected, user will wrongly use the scale. Little things mean a lot.

4 comments:

  1. What is the CRS of the point data layer?

    I'm not exactly sure what the error is here...

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    Replies
    1. Well actually there is no error in the sense of the word. The point I wanted to stress especially among new users is not to assume all default setting is as what they wanted it to be and on-the-fly projection is something new among new users and that if layers were created with the assumption that it was 'off' but actually was 'on' then later when the on-the-fly projection is unselected, they may start to complain why the GIS software made their map projection wrong whereas they should have unselected it in the first place when that layer was created.

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    2. Ah! Gotcha! Be sure to point out that the new point file that was created was in a local coordinate system - I'm guessing - which is what turned the 'on the fly' back on...

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    3. "which is what turned the 'on the fly' back on..."

      That's a good question indeed. It seems to as if QGIS has the ability to zip up its trousers every time it leaves the toilet.

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