It has a very simple but long answer.
First some of the answers before are correct actual cartography is occidental and conventional.This answers the WHO
WHEN: There was a time not long ago, still around the 1600´s where every map system had a different center or starting point of reference. That is why there was so much spying in, say, Columbus times, because not only their maps were highly secret even thoughl the spanish maps took Madrid as the 0 meridian and coordinate system, the french had Paris, the english greenwich and arab maps Meca, and so forth. Visit any old map site and see what country is in the center of the map and the relation with the origin of the map.
WHY: After a while, when most routes where open around the world and there was no reason the keep them secret, they got together, some Occidental powers that is, and conveened arbitarily, or by arbitrium - or consense- to chose one 0 meridan that was the same for all. I do not know if they flipped a coin or they just used all type of leverage between each other but at the end they chose Greenwich as 0 meridian.
Wrong: Some scientists say that it is due to the magnetic polarities of the earth, but this is not ont only bolony but is untrue since the magnetic polarities of the earth fluctuate and change continuously.That is why when Columbus sailed towards America (which by the way should be called Colonbia, Vikingia, or to be New Mongolia, since mongolic peoples were the first to cross into america via the frozen bering straight, and hence are the ascenstors of american indians, and got there first) well Columbus noticed that his instruments were giving very different readings that were not logic. The changes in magnitudes around the equator where fluctuating and his quite basic instruments going Bananas.
So he wandered why this was.
If nor australians or canadians fall into space, because of gravity, the position of the whole universe is again arbitary and has names which differ in many languages. Just take any earth globe and put it upside down on its holding axis and you will understand that basically nothing changes just there is a translation of 180 degrees but the universe remains the same. Again an occidental conventional system.
PERCEPTION ERRORS: Now when we look at the the sky due to the speed of ligh we are seeing elemets that do not exist sumulataneously in time because space is flat, according to Einsteins relativity, and for exaple moon is quite close and the ligh (image) of the moon arrives to our eyes in x time however in the same field of view there are other lights, and these light take a Y period to arrive to our ayes. The light of this stars that we see as existing simultaneously with the moon originated in stars or constellations systems that are not there anymore, because, either they have moved or they do not exist anymore. Yet for us they exist simulaneously. So it is like if we took a photo of the sky different nights different days and different years and we used a graphic design program to make all the different photos, or layers, blend together and they would appear to exist all simultanously. Yet they are not. If we can make so huge errors evaluating somethings as apparently simple as the heavens, Imagen what kind of mistakes we can make with other more complex or confusing decisions.
I am occidental, and have no desire to discredit our culture or any guilt about these facts. However, the truth is how it is, we like it or not. Most people oriental or occidental do not give a rats **** about these issues.
I myself have by home globe upside down and teach my children that that white ball up there is not the moon, but something, which we know very little about, and which english speaking persons call moon I call Luna. And their mother calls Kuu. Yet the ball is not the moon.
I also have all maps in my walls upside down and have memorized world maps so I can draw them accuratelly upside down. Why,? Because scientists are not only dumb but to proud, and some humbleness would help threm learn something more and is quite OK.
All present and past knowledge about the world and everything on it is arbitrary, from numbers to medicine. It has been consensed for whatever reasons, sometimes good, sometimes bad, sometimes for convenience or time pressures, yet north, south, east, west do not exist per se, they are just human artificial constructs, of the english language. In fact North in Finnish is Pohjois, South is Etela, East is Ita and West is Lansi, so you see in Finland there is no north, south etc.
All the science today is first based in language and sign systems which are all conventional and arbitrary and are underfunded. Already Protagoras of Samos, several hundred years BC, argued that 1 +1 = 3, and he was partly right, (too long to explain here) but I suggest you read some bokks on set theory and the disagreements between Mathematicians therein.
Then the astrophisicists, who are bummed out that particle phicisits have told them all their knowledge is bullshit, get together and since any news, is good news, their stripe pluto of ts condition of planet,
Why? To get noticed, since there is no reason not to consider Pluto a Planet. First because they themselves have been working and work till this day without an operational or theorectical definition of what is a planet.
Second since Pluto shares more characteristics with other planets in the solar system than let us say, Jupiter, which is a ball of gas...And even though there is no reason to strip Planets of their planethood. they will do anything, even ,ake their theoretical forefathers look like sh.... to get noticed.
WHY: If all these was of public domain, which by the way it is since it is all published in books, which are hidden at plain sight between millions of other books, and clearly understood then the thousands of millions of dollars spent in research, while so many die of hunger, for example, looking for something called black matter which no one has ever seen or detected with any machine, would have to be stopped and they would loose their jobs prestige etc.
Same reason if I ask exactly where does the heart ends and the aorta begins, since they are integrated, we would have to agree arbitarily and maybe someone would notice that the scientific status quo is in trouble,and some more dudes without a job, and many priviledges,
And no one would move aside when some man shouted Out of my way I am a Dr.....
So this is HOW it is, WHEN it happened, WHO did it and many reasons WHY, I could explain in more detail some of the thesis advanced here but it would be too time consuming for this forum and a virtual relation. Best wishes anyway
San2