From the article:

"It was observed already many years ago that this 'Giza diagonal' might have had a symbolic meaning, since it points in the direction of the city of Heliopolis, north-east of Giza (according to Jeffreys (1998), the first mention of this fact is contained in a 1852 map by J. Hekekyan)."

Magli does not give the Hekekyan reference in his footnotes. The Jeffreys reference is given as "The topography of Heliopolis and Memphis: some cognitive aspects," in Beitrage zur Kulturgeschichte Aegyptens, 1998.

Unfortunately I do not have access to this journal.

Any help?

Googling turned up the following articles by or about Hekekyan:

* Notes on the Eastern desert of Egypt, from Gebel Afret, by the ancient porphyry quarries of Gebel Khan, Near to the old station of Gebel Gir - with a brief account of the ruins at Gebel Khan - by Hekekyan bey - Journal of the Asiatic Society of Bengal, November 1848, pp 584-587

* A treatise on the chronology of siriardic monuments demonstrated that the Egyptian dinasties of Manetho are records of astrological Nile observations which have been continued to the present time, by Hekekyan bey C.E. of Constantinople - formely in the Egyptian service (for private circulation) London, printed by Taglar and Francis 1863, I vol, 160 pp

* Ahmed Abdel-Rahim Mustafa, The Hekekyan Papers, pp 68-75, in "Political and Social Changes in Modern Egypt", P.M. Holt, London 1968

* Darrell I. Dykstra, Joseph Hekekyan and the Egyptian School in Paris, The Armenian Review (Boston, USA), 1982 N#35, pp 165-182

* Jeffreys, David G, 2000. Joseph Hekekyan at Heliopolis, in A Leahy & J Tait (eds), Studies in honour of H S Smith. London 1999, pp.157-168.

[www.crda-france.org]