Between 1468 and 1480 Benincasa made 9 atlases with maps in it with the Cabo Verde Islands on them. A few weeks ago I learned that one of them is in color. This week I learned that two more are in color too. Now I want to have a copy of all nine maps. I guess they are all in color. I want to compare them and find out how accurate they are.
According to Roel Nicolai (more) portolan charts are based on a mathematical model which closely resembles the Mercator projection and not on the input of observations of seaman coming back from their travels. The maps were first. Out of the blue as far as we can tell now.
Today I puzzled at the G. Benincasa 1473 'Egerton 2855' map.
(C) The British Library Board, G. Benincasa 1473, Egerton MS 2855 ff.6v-7
Conclusion. The distances on this 541 year old map are pretty reliable: average 119% with a standard deviation of 35.
What's next? I want to find out if the maps improve in time. Are the maps of 1480 more reliable than of 1468? In other words, projection first - out of the blue - and then the maps get better every year because the input of the seaman, returning from the sea, was digest by the mapmaker G. Benincasa?