Wayfinding is an essential human skill. This task can be accomplished by reference to key positions for the sun and the stars in relation to the earth.
A useful tool to aid in orientation is a map. The standardisation of cartographic conventions lets people share important navigational information with others. The convention for orientation in the Indus Valley Civilisation was that north-west was placed in the centre at the top of a map or diagram¹.
If everyone can locate the position north-west in a diagram, it follows that they can also locate each cardinal point in the diagram.
For image credits, please see below.
The Indus script combines the known convention for navigational points with the concept of duality, in the form of a point of light or a point of darkness, to impart useful information. Some examples of this are given below.
Relative Position in Relation to Dim Light:
This symbol is a point of darkness located to the north-west of the character area. In the Northern Hemisphere, the midsummer sun sets to the north-west. Hence, this is an ideograph for the transition from light to dark.
The ideograph was used in a similar way to the modern Chinese character yīn 陰 to indicate the shady side of something. A good example of this usage in Chinese is Huàyīn 華陰, the name of a city situated to the north of Mount Hua.
Illustrative Text References:
Harappa: Seal: H-1048 a (NB. Indus sign number 99 is clearer in image A): Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 145: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-314 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 78: Collections in India: Suomalainen Tiedeakatemia.
Comments:
In inscription H-1048, the women are working in the shade of a tent. In other words, inside or within a tent. Whilst in M-314, the literal phrase 'cart load in' refers to the make-up of a consignment.
Relative Position in Relation to Bright Light:
Light marks the centre of the character area. It is the point where the subject is located. It is the noun spot, location, or place.
This symbol shares the same root as the Chinese character zhǔ 丶.
Illustrative Text Reference:
Harappa: Seal: H-1710 A (There is no view a): Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 238: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Composite Characters:
If a word is placed in the centre of the character area, and surrounded by four points of light, it indicates that the statement is true at each of the cardinal points. In other words, the four points of light are an ideograph for the adverb everywhere.
The illustrative example on the left, is the verb: to trade with the adverb everywhere. Therefore, sign number 404 means to trade or to sell everywhere.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-626 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 7: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credits:
Indus Script Signs with Numbers: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.
Orientation and Cardinal Points: Lynn Fawcett, 2017.
Note:
1. My hypothesis is that the convention whereby north-west was placed at the top of a diagram was not unique to the Indus Valley Civilisation. A surviving example from elsewhere (although a later period) is the clay tablet, with an incised plan of the city of Nippur, currently held in the Hilprecht Collection at the University of Jena.