Good example of visualization
The above picture was prepared by the European Environmental Agency (EEA). The Report has been requested by the Ministers of the Environment of all European Countries to be presented in Ärhus (Denmark), June 1998. The display shows the fresh water availability per capita in the different European countries.
this graph uses the background color in a nice way so we can intuitively see which countries are in the dry zone and which countries have plenty of water. In addition, it sorts the countries according to the water generated within the country, and puts the visual emphasis on that, yet we can still easily see which countries have more water from river flows from other countries.
Bad example of visualization
source: www.trade10.com/ momentum_trading.htm
The above graph tries to illustrate success of a theory of predicting stock market trends. White bars indicate it was an up day, while black bars indicate it was a down day. The bar indicates the opening and closing numbers of the day, and the line indicates the fluctuations during the day. the blue dots are the days which predict a change in trend which succeeded, and the red dots indicate that there was a prediction of a change in trend that failed.
This graph is very poor in my opinion. first, the use of black and white color for up and down days is very confusing and not intuitive. We need to remember these notations, and furthermore, remember that the closing number for the up days is the top of the white bar, while the closing number for a down day is the bottom of the black bar. in addition, there is much clutter in the graph, which prevents us from seeing what the graph is meant to show. the information about the up and down and the fluctuations of the day are not needed to illustrate the point which was that the prediction days according to the theory work well. To show this theory, it was better to show one point (end of day for example) every day.