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Who discovered the Great Salt Lake?
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[QUOTE]Originally posted by NaturalResources: [QB] Tex, I agree. At first glance it does appear that the Great Salt Lake would be to the north and east of the location I have marked with the red arrow based on its relation to other features of the North American continent as shown on the 1593 De Jode map. However, closer examination of the lat and lon of the lake reveals something that is either a complete coincidence, OR was intended by the cartographer of this map. The lat and lon of the lake I have shown is ~42N lat, ~263E lon. The modern lat and lon of the GSL is ~42N lat, ~112W lon. When this map was made, cartographers often gave longitude only in degrees east of the prime meridian, so if we want to compare the two, we have to either convert the modern lat and lon of the GSL to the 1593 lat and lon used on the map, or the lat and lon of the lake on the 1593 map to modern lat and lon of the GSL. In my example, I will convert the modern west lon of the GSL to degrees lon east, as is used in the 1593 map and compare it to the lake I have shown. Prime Meridian = 360 Modern GSL lon = -112deg (or 112W) 360-112 = 248deg (or 248E) Therefore the converted modern GSL Lat and Lon is 42N lat, 248E lon. If you compare this to the lat and lon of the lake featured on the 1593 map, (42N lat 263E lon) you will immediately notice that the latitude is exactly the same, while the longitude is off by only 15 degrees. However, one more step must be taken before you can correctly convert modern lat and lon to the lat and lon used on the 1593 map... Before the "Universal" Prime Meridian was established in Greenwich England in 1851, the location of the prime meridian varied from country to country and map to map. While the Dutch Cornelis De Jode 1593 map does not show where the prime meridian is, IMO it is reasonable to assume he used the Cape Verde Islands as his prime meridian, a common practice by Dutch mapmakers all the way up until the late 17th century. The Cape Verde Islands have a modern lat and lon of ~15N lat, ~23W lon. This means that the prime meridian used in the 1593 map is 23 degrees west of the modern prime meridian in Greenwich. To correctly convert the modern lat and lon of the GSL you must also add 23 degrees to the longitude east because you are moving your prime meridian 23 degrees to the WEST compared to the modern prime meridian. Modern GSL lon in degrees east before PM adjustment = 248 PM adjustment = 20 248+20 = 268 Thus, the converted modern lat and lon after adjustment for the Prime Meridian for the GSL is ~42N lat, ~268E lon, or only 5 degrees different from the lake featured on the 1593 map. In addition, the fact that the latitude is dead on and the only "error" is in the longitude makes sense considering how much more difficult it was to deterimine longitude than latitude at that point in history. To me, this suggests the lake shown on the 1593 map was intentionally placed there with full knowledge that a lake did indeed exist at that particular location. BTW, I have been working on a graphic to present this information in visual form because I have found it can be very confusing trying to explain verbally. I hope I have done an adequate job here, and I'll try to post the graphic when I finish it. NR. [/QB][/QUOTE]
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