Maps et al Mystery Cache

Where do maps REALLY come from?

Nicholas Louis de la Caille, was a French astronomer-geodesist, and is one of a long line of pioneers that established and moulded the first South African trigonometrical Survey. He arrived at the Cape of Good Hope in 1751. His mission was to catalogue the southern stars by celestial co-ordinates of right ascension and declination. These observations were made from a house in Strand Street, Cape Town, owned by Mijnheer Bestbier. Take a look at an interesting geocache hidden on the site. Astronomical Heritage:La Caille (GC2MXGZ)

His observations resulted in the cataloging of 9 766 stars and 42 nebulae. Including the star constellation Mons Mensa or Table Mountain which is the only constellation named after an inanimate object. His task completed he had time to kill and so set himself another challenge. The length of an arc of meridian in the Northern hemisphere had been accurately measured but no such measurement had been done in the Southern hemisphere. If an arc of meridian in the Southern Hemisphere was equal in length to an arc of meridian in the Northern hemisphere it would be conclusive proof that that the earth is shaped like a slightly flattened orange squashed at the poles and wider at the equator.

There are precise survey methods to do this and he proceeded to execute them north of Cape Town (Zwartland). One of his measuring points is in Aurora where there is a monument built in his honour by this department. There is a geocache PEARSHAPED OR ROUND? (GCRP1N) hidden close by. As it turns out, his measurements and calculations were flawless and he succeeded in proving that an arc of meridian in the southern Hemisphere is LONGER than an arc of meridian in the Northern Hemisphere. In other words, La Caille’s calculations showed that the earth was shaped NOT like a flattened orange but rather like a pear!! We now know that his proof was incorrect but at the time it puzzled mathematicians and Geodisist around the world. They checked and rechecked his procedures and calculations but they were all perfect. It took many years before this incorrect conclusion was recognized by Sir George Everest of Mount Everest fame (see pic below) during a visit to the Cape in 1820 and later rectified by Sir Thomas Maclear.

La Caille’s mistake was that he had not considered gravity. Much of his measurements were taken in the mountains and unbeknown to him, the minuscule increase in gravity caused by the heavier mass of the mountains caused his plumb line to lean slightly. Not being vertical, his measurements were slightly out and hence the conclusion of the pear shaped earth. Maclear arrived in South Africa in 1834 and re-measured the arc of meridian that the Abbe de la Caille originally measured. He had been warned by Everest of the effects of gravity and wasn’t fooled by the effect of gravity when doing his measurements and calculations. And so a 90 year old mystery was finally solved. The full story can be read here. Sir Thomas Maclear can be seen pictured below.

While Maclear was solving Abbe de la Cailles conundrum he also started extending his measurements north and south and in doing started the process of measuring and mapping South Africa by establishing known points in prominent places. These known points are in the shape of white pillars adorned with black vanes on the top known as Trigonometrical beacons and there is a geocache Maclears Beacon (GCW84K) on top of Table Mountain hidden next to a trig beacon dedicated to Sir Thomas Maclear. The Trig Beacon pictured below is in Port Elizabeth and is an important one as it is the terminal point of the extention of the 30th Arc Meridian. A project that was intiated and performed by this office. There is a geocache hidden in the immediate vicinity. Another cache associated with the arc of the 30'th meridian is Arc of 30th Meridian #13 - Hluku (GCGXOQ). But thats another story.

In 1927, the government at the time saw a need to maintain and extend this system of known points or trig beacons throughout the country. Legislation was passed that saw the establishment of a national organization specifically dedicated to extending, densifying and maintaining these Known points to cover the entire country. This organization has gone through many changes but at the moment is called “National Geographic Information” (NGI) and resides under the Department of Rural Development and Land Reform. The two pictures below depict the building in the 1950's and the new revamped one in 2011.

This organization is mandated to photograph and map South Africa every 3 years. To do this they have to overfly South Africa continuously every year in order to keep up with data collection and keep their maps topical. They have been doing this on a continuous basis since 1944 and have archives of aerial photographs dating back to 1945. Their core product is a 1:50 000 topographical map and a 1: 10 000 Orthophoto map. Both of these products among others are available for free. The small charge incurred is to recover the cost of the medium that the maps are printed on. More information can be obtained here. There is a small museum at the offices of the NGI and visitors are welcome to come and look at some of the old surveying equipment that was used back in the old days. Of course much of this has been superseded by GPS and are little more than museum pieces banished to the annals of history by the march of time and advancements in technology.

It seemed apt for me to hide a geocache close to the building that has long been known as “Trig Survey” by people needing maps for their journey in the days before GPS. The published co-ordinates if looked at using Google earth will take you to the courtyard in the middle of the building and shouldn't be used as a starting point for the hunt.

There are three questions that have to be answered in order to get the co-ordinates that you need.

1) Before planes were used to carry cameras, various experiments using birds were attempted. How many letters make up the type of the bird that was experimented with? (A). The answer can be obtained here

2) What year was South Africa’s first satellite “Sunsat” launched? (199B). The answer can be obtained here

3) How many letters are in the acronym for the generic term of ALL the satellite systems in use today? (C). The answer can be obtained here

The co-ordinates are S 33 57.0(A-C)(B-C) E018 28.(B-A-2)(C+1)(B-C-5)