Google Insights for Search* picks up quantitative data from the internet with given filter and search terms. The chart above is the search result from: terms berlin wall, berliner mauer; Worldwide, 2004 - present; covering categories: Arts & Humanities, Entertainment, Local, Society, News & Current Events, Reference. Two trends emerge here for the English term "berlin wall": showing a peak in November 2009, 20th anniversary of the Wall being breached which accumulated global interest; as well as repeating global pattern, where every May sees the highest buzz of the year. In contrast, "berliner mauer" (German for the Berlin Wall) sees more an evened out trend, with an increase, over the anniversary.
*The Search analyses a portion of worldwide Google web searches from all Google domains to compute the number of searches that have been done for the terms that you've entered, relative to the total number of searches done on Google over time. You can choose to see data for select Google properties, including Web search, Images, Product search and News search (certain properties aren't currently available in all countries/territories).
On the results page, you'll see:
a graph with the search volume, indicating interest over time (GMT) for your terms, plotted on a scale from 0 to 100; the totals are indicated next to bars by the search terms (read more about how we scale and normalise the data)
a breakdown of how the categories are classified
lists of the top searches and top rising searches
a world heat map graphically displaying the search volume index with defined regions, cities and metros
Keep in mind that Insights for Search uses data aggregated over millions of users without personally identifiable information and is powered by computer algorithms. In addition, it only displays results for search terms that receive a significant amount of traffic and enforces minimum thresholds for inclusion in the tool.
Google Insights for Search (2010) Web Search Interest: berlin wall, berliner mauer. [Online]