Data cleaning limitations of QGIS
Data cleaning is important to ensure that data is accurate and it is often assumed especially by those who have not done hands-on with any GIS that any GIS software can rectify all sorts of data cleaning thrown to them, after all, if it can create a GIS layer, it sounds ludicrous that GIS software cannot repair any type of GIS error and if you were to tell such person that QGIS cannot do it, the immediate reaction would be "What a hopeless GIS software QGIS is! I made a grave mistake and am definitely sure proprietary GIS is better". The reality is that QGIS adopts the same simple vector feature topology as ArcGIS and Mapinfo to name a few so the problems faced by them on matters of data cleaning are the same. So the next question will be "What are they?" I am still doing my homework on this and for the moment what I see are as follows:
Although auto-cleaning tools may exist in some GIS software, it is probable that rules associated to it do not make them as accurate as on the ground. Unless there is supporting data to guide and identify the accurate side of the gap e.g road, river, surveyed layout plan etc. your guess is as good as mine whether to move the left side of the gap to the right side of the gap or vice versa. Snapping options will help in this error.
Overlap error suffers the same problems and fate as gaps and snapping option does the same job here.
|Nodes that do not meet|
Nodes that do not meet
Overlap error suffer the same problem and fate as gaps and overlaps, again snapping option helps.
One to many scenarios
Limitations of the desktop GIS software not to allow the creation of sub-rows means such problems cannot be resolved. The solution is to migrate to an RDBMS unless someone has a better answer for the desktop GIS software. Hello...anyone?
The desktop GIS software does not have the capability to automatically measure the length of the hypotenuse but in fact measures the horizontal distance thus always gives a less than accurate measurement of the hypotenuse distance. This problem seems very obvious to me but I am surprise this has to my knowledge ever been made known in any Q&A and FAQ sites. I honestly do not know how to resolve this.
Another problem also is the need to find a tool to that can easily identify topology errors in one go. I've tried geometry tools/geometry validity but it does not tell what type of error were identified so that's a big drawback. Another alternative is to venture into GRASS Modules but I don't intend to elaborate on this for fear that this may turn off prospective QGIS users.