Why do maps change so much?
Cartography (map making), has been around for thousands of years. When people first got around to making maps they were relying on visual clues and their own hands to make maps. If you're like me (and have no knack for drawing) it's very easy to misrepresent something like a coastline when you're trying to draw it yourself. Maps represent the interpretation of the world at the time it was made. Gradually as technology and knowledge about Earth's surface progressed more accurate maps could be made. For example, it's hard to have an accurate portrayal of the globe if you don't know about the Americas. And it's hard to accurately represent the position of continents on a flat map when they curve around the Earth. In the last century we've made great leaps and bounds in map making, we can now take digital pictures with satellites. We can accurately accommodate for the curvature of the Earth. We can measure mountains, canyons, rivers, inlets, and coastlines with more accuracy. Maps change and have changed because our spatial awareness has changed. And they will continue to change as more advancements are made. Perhaps it's safe to say our view of our planet is pretty accurate, but we're mapping Mars, our solar system, and even our ocean floors...and as we learn more, our maps and interpretations of those places will change as well.
Why is World History so European centric?
World History relies so heavily on Europe because there is not a single corner of the globe that European powers haven't touched. Additionally, European influence in non-European corners of the globe mark great changes in those societies, so it's very important to focus on those changes to learn how we got to where we are today. Europeans never simply found a new piece of land or a new people and left them alone; they colonized and exploited everything they came across. That being said, there is a lot to learn about indigenous cultures that modern (European centric) world history tends to ignore.
What are the major difference between Western and Eastern Europe?
To put it simply: language and religion. It all stems back to the fall of the Roman Empire (476 CE). When Rome fell, the eastern half of the empire remained intact. This half would soon be called the Byzantine Empire. Eastern Europe was largely influenced by Greek culture. The languages of Eastern Europe almost exclusively use the Cyrillic Alphabet, which was developed from the Greek Alphabet. Western European languages (and the alphabet they use) were developed from the Latin language and alphabet. As for religion, that also goes back to the fall of Rome. Just prior to the fall of the western half of the Empire, the Romans had divided territory into the Eastern and Western halves. They essentially installed two Emperors and said they co-ruled, but each stayed on their side. The Roman Emperor(s) were also the head of the Catholic Church. There were many disputes over how Christianity was supposed to be practiced. After Western Rome fell, the Patriarch of Constantinople (Eastern Empire) and the Pope (Western Empire) tried to excommunicate one another. This resulted in The Great Schism (1054 CE). Thus Eastern Orthodox Christianity is practiced in Eastern Europe, and Roman Catholic Christianity is practiced in Western Europe. Language and religion do a lot to influence culture. In modern Europe, there are many new languages and religions spanning the continent, but when you look back far enough these were the major divides that made Eastern and Western Europe two very distinct places.