The North-west Convention and Bronze Age Traders
My hypothesis is that trade in the Bronze Age may have been assisted by the adoption of an international standard for map and plan making whereby the direction north-west was placed at the top of the plan.
A good example of such a plan is the town plan for Nippur, which was incised on a clay tablet dated to around 1,500 BCE. Jim Siebold states that Miguel Civil found the orientation of the map to be north-west to south-east¹. Civil's conclusion is supported by the orientation of the writing of the label for the temple. If the plan is orientated so that the temple's name is set horizontally, the direction at the top of the plan is north-west.
Another example is the Bedolina map in Val Camonica, Italy. The date of this map is disputed, but it too may date from around 1,500 BCE².
A little earlier in time (perhaps 2,800 BCE), the north-west convention hypothesis is supported by the symbols on the left from the Ness of Brodgar³.
In the centre is the verb to call or to cry out, which shares a common root with the Chinese character xuān 吅. It is comprised of two voices, one of which is placed at the top of the character area (in the north-west), and one of which is placed at the bottom of the character area (in the south-east).
The voices are placed inside an enclosure. Hence, we have an ideograph for a structure from which the time of sunrise and sunset is called.
The first enclosure is surrounded by a second perimeter wall, which represents the settlement at the Ness.
Finally, there are two bodies of water, which represent what is now the Loch of Stenness to the north-west, and the Loch of Harray to the south-east.
There is also a much older example, in the form of an engraved pendant, from Starr Carr in the United kingdom⁴. The top of the map is marked by the hole for the cord from which the pendant was suspended. This map is dated to the Mesolithic circa 9,000 BCE.
The convention for placing north-west at the top is incorporated into any Indus character where directions are relevant to the meaning of that character.
Notes:
1. Jim Siebold: Monograph: City Plan for Nippur: http://www.myoldmaps.com/maps-from-antiquity-6200-bc/101-mesopotamian-city-plan/101-mesopotamian-city-plan.pdf: Accessed: 9 November 2018.
2. M. Beltran Lloris dated the map to around 1,500 BCE, but Christina Turconi argues that it was probably created in the Iron Age: Christina Turconi, 1997: The Map of Bedolina, Valcamonica Rock Art: TRACCE no. 9: http://www.rupestre.net/tracce/?p=2422: Accessed: 12 June 2019.
3. Symbols from the Brodgar Stone, which was found in 1925: http://www.nessofbrodgar.co.uk/brodgar-stone/: Accessed: 3 July 2019.
4. The Pendant: http://www.starcarr.com/pendant.html: Accessed: 3 July 2019.