Well, I am taking a back seat in this CWBP so its all up to you but it would seem odd to me to have a world map that is broken up into chunks where the plots are then of different scales.
I thought the idea would generally be that you could walk off of one plot and onto your neighbors and that the roads and terrain would be at the same scale. Its as though the underlying world is there as one thing but you all go in a map it differently - not that the underlying world is different per plot.
Seems to me that if you had different scales per plot then you might as well have 50 random plots that don't butt up at all.I thought that the scale was 1 pixel is 4 km at the equator dropping to 0 at the poles in the usual Mercator style. The problem with mapping a globe is that you have curved space. If the plots are small enough then you can select the scale from the middle point of the plot and then make it that all over the bitmap and accept the slight distortion. Or as mentioned before, you can reproject it (gdal etc) to something of equal area and then transform it back again. Note, I wouldn't do this as its too much hassle but its an option. So choose small plots and the issue goes away. But yes, a house at the pole will stretch all the way across the world map since the pixels there map near to a point at the poles.
I think one of the big differences between the old and new coop discussions are that here it seems that people believe that once all the plots are taken its all done. I think what was understood more clearly - well ok maybe just discussed more frequently - is that other people would come along and take a plot regional map and then map something of larger scale within it, like a city for example. Maybe it would help if I pointed people at my vid I made of the last CWBP showing the state of play near to the end. You will see that its just not possible or sensible to map cities within the plots in the top most plot map and that you will necessarily have to go down a level and make more maps within it. So there are only going to be regional maps at the plot level since any city at the equator of a size less than 4Km will be mapped with one pixel.
I say again - you don't have to follow what happened before. I'll try to fit all the maps together with my app if they are supposed to fit together. And I would suggest to people to have a little think about what one pixel means at the world scale on their plot. If you took 200 pixels of world map plot size at the equator area and then made a 4000 pixel map from it then your 4000 pixels mean 200 * 4km or 800km or 1 pixel is 200m. So features should represent that kind of scale - so not really suitable for houses etc.
Do you know I have reread the thread again and got a different impression here about what is being asked. Ummm - the scale is changing as you go vertically up and down the world map but that they are the same scale at a border between neighbors. So its the same scale in a world projected map but since the world is global and curved its changing across the map vertically. And yes you should deal with that so my opinion is to choose small plots and pick the center pixel as the scaling. I'll so another post with the scaling math...