Comment to project managers of Building projects

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Comment to project managers of Building projects

john whelan-2
A snapshot of 10% of Uganda gave me 870 duplicate buildings. This is where two buildings overlap by more than 50%. This is merely to give you an idea of the scope of the problem.

If you are relying on the data then running Mike Thompson's detect building script will find any duplicates in your project.

Typically I'm seeing clusters of up to 200 duplicate buildings in a small area, that one was on a project to count buildings for a solar panels. These are not uploaded twice but the buildings have been mapped twice with small differences.


Select Duplicate Buildings 
Selects duplicate, or near duplicate, area buildings in JOSM's active datalayer.
A "near duplicate" is a building whose area overlaps another building's
area by more than 50%. Only the first building encountered of an 
overlapping pair is selected. This is done so the issue does not have to be 
looked at twice. The selected buildings are added to the current selection.  
Currently only works with buildings that are ways (not multipolygons).

To Run:
* Install JOSM's Scripting Plugin (only necessary once)
* Place file in a convenient location on your system (only necessary once)
* Click "Scripting" (on top menu bar)
* Click "Run"
* Click "..." button and select the script file.
* Click "Run"

If you decide to delete some I'd recommend downloading the area fresh in JOSM then running the script, inspect each building deleting if need be then upload the results quickly to reduce the risk of a another mapper deleting the other building of a pair. 

Cheerio John

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Re: Comment to project managers of Building projects

Bjoern Hassler
Hi John,

Thanks for this suggestion.

Would it be an idea to enhance the mapathon instructions, to include suggestions such as running scripts like these (at the validation stage, or perhaps run by the task owner)?

If anybody wants to get together to discuss those planning/ best practice-related issues, I'd be very happy to  join in!

Bjoern

On Wed, 27 Dec 2017 at 19:12, john whelan <[hidden email]> wrote:
A snapshot of 10% of Uganda gave me 870 duplicate buildings. This is where two buildings overlap by more than 50%. This is merely to give you an idea of the scope of the problem.

If you are relying on the data then running Mike Thompson's detect building script will find any duplicates in your project.

Typically I'm seeing clusters of up to 200 duplicate buildings in a small area, that one was on a project to count buildings for a solar panels. These are not uploaded twice but the buildings have been mapped twice with small differences.


Select Duplicate Buildings 
Selects duplicate, or near duplicate, area buildings in JOSM's active datalayer.
A "near duplicate" is a building whose area overlaps another building's
area by more than 50%. Only the first building encountered of an 
overlapping pair is selected. This is done so the issue does not have to be 
looked at twice. The selected buildings are added to the current selection.  
Currently only works with buildings that are ways (not multipolygons).

To Run:
* Install JOSM's Scripting Plugin (only necessary once)
* Place file in a convenient location on your system (only necessary once)
* Click "Scripting" (on top menu bar)
* Click "Run"
* Click "..." button and select the script file.
* Click "Run"

If you decide to delete some I'd recommend downloading the area fresh in JOSM then running the script, inspect each building deleting if need be then upload the results quickly to reduce the risk of a another mapper deleting the other building of a pair. 

Cheerio John
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Re: Comment to project managers of Building projects

john whelan-2
It was more of a heads up comment about data quality.  Certain projects use building counts to estimate population for one reason or another.  The one I spotted was about did it make financial sense to install solar panels.  So if you count the number of buildings this gives you an indication of demand.

However for some areas if you count the number of buildings in OSM you are counting the real buildings twice.  So if your project depends on knowing an accurate number of buildings then I suggest you run the duplicate building script to ensure none are counted twice.

So its very much aimed not at maperthon organisers but at the people who use or analyse the data.  It's a way to strip out some of the errors.  Project managers perhaps.  The problem with maperthon organisers is not all of them know how to map so they aren't a good target audience.  The project managers need good accurate data so they are the ones who would be motivated to do these sort of checks.

I don't think we need worry too much about it.  We have a tool to spot them and I've probably deleted a thousand or more already and others will be cleaning up the map so hopefully they'll disappear in time.

If we extended the time lock on a tile to four hours that might be enough to prevent a few or if we can get people to upload every thirty minutes that might eliminate some.  The real problem here is the number of extra buildings that could have been mapped with the same amount of effort.  Say it that way and you might catch a few maperthon organisers attention.

The problem with validation is as soon as you come up with a basic set of tests then someone comes along with a new twist.  Using JOSM to check for untagged ways, crossing highways, highways terminating close to another highway, unclosed buildings, duplicate ways. e-arching for highway=road is fairly quick and simple plus scanning the tile to see that everything has been done to a reasonable standard.

Adding in things like highway=yes, or ways tagged highway=unclassified, building=yes can be done but adds to the time taken when validating.

Cheerio John

On 27 December 2017 at 17:23, Bjoern Hassler <[hidden email]> wrote:
Hi John,

Thanks for this suggestion.

Would it be an idea to enhance the mapathon instructions, to include suggestions such as running scripts like these (at the validation stage, or perhaps run by the task owner)?

If anybody wants to get together to discuss those planning/ best practice-related issues, I'd be very happy to  join in!

Bjoern

On Wed, 27 Dec 2017 at 19:12, john whelan <[hidden email]> wrote:
A snapshot of 10% of Uganda gave me 870 duplicate buildings. This is where two buildings overlap by more than 50%. This is merely to give you an idea of the scope of the problem.

If you are relying on the data then running Mike Thompson's detect building script will find any duplicates in your project.

Typically I'm seeing clusters of up to 200 duplicate buildings in a small area, that one was on a project to count buildings for a solar panels. These are not uploaded twice but the buildings have been mapped twice with small differences.


Select Duplicate Buildings 
Selects duplicate, or near duplicate, area buildings in JOSM's active datalayer.
A "near duplicate" is a building whose area overlaps another building's
area by more than 50%. Only the first building encountered of an 
overlapping pair is selected. This is done so the issue does not have to be 
looked at twice. The selected buildings are added to the current selection.  
Currently only works with buildings that are ways (not multipolygons).

To Run:
* Install JOSM's Scripting Plugin (only necessary once)
* Place file in a convenient location on your system (only necessary once)
* Click "Scripting" (on top menu bar)
* Click "Run"
* Click "..." button and select the script file.
* Click "Run"

If you decide to delete some I'd recommend downloading the area fresh in JOSM then running the script, inspect each building deleting if need be then upload the results quickly to reduce the risk of a another mapper deleting the other building of a pair. 

Cheerio John
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