Hi,

The idea is for sure to check the date of the imagery and map when new imagery 
are available and we can consider also the time step between the different 
satellite imagery.

The fact that some contributor modify the data is not a problem because they 
will done adding new information and this is just an improvement in the data.

Think like they are highway, I can’t known what is the type of the highway but 
I can cleary see that its a road, so I can map it as highway=road with all the 
problem of this case. But un other user with better knowledge can identify 
which type of highway.
In a similar way there is just a different structure of classification, and 
when better imagery or generally better info are available the tag landcover 
will be improved with the more detailed tag.

For what regards the history I’m agree with Martin.

Best,
Lorenzo


Il giorno 15 mar 2019, alle ore 08:32, Joseph Eisenberg 
<joseph.eisenb...@gmail.com<mailto:joseph.eisenb...@gmail.com>> ha scritto:

> “The idea is to have mapathon in
> different time, when new imagery are
> available and after check what
> changed searching in the database

In this case you only need to map the area of woodland or forest now, and it’s 
no problem to leave other landuse and natural areas unmapped.

But it may be difficult to use the OSM database for checking changes over time, 
if you would like scientific, publishable results.

To properly compare the current woodland area with the area in a couple of 
years, you will need to make sure that the aerial imagery that you use now is 
all from the same year.

Then, when you repeat the project in 1 or 2 years, you need to have new imagery 
from around the same time, and you should map the woodland or forested areas 
using the same standard and methods as they first time. This will be easiest if 
you remap everything from scratch the second time as well.

If you try to use the OSM database both times, you may find that other mappers 
have changed things in the meantime. Perhaps they have changed some of your 
landuse=forest to natural=wetland wetland=mangrove, because they know the area 
better. Perhaps they have mapped a new palm
oil plantation based on local information, but it isn’t visible in the aerial 
imagery. How will you deal with such changes?

So it is great to add the forest or wood areas to OSM right now based on the 
latest aerial imager.

But you should plan to keep your own copy of the database to compare with and 
edit in the future. If you do this right it could be professionally-quality 
data for environmental research, but that means you need to keep a copy of the 
data that won’t change, and use that for comparison in the future.

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