Data Over Time

Data over time is a type of data visualization that represents how the data is changing over time. The types of data visualization that show data over time being discussed on this website are a stream graph, a histogram, and a heat map.

Stream Graphs show change in data over time through the use of organic shapes, which increases the visual appeal. The shapes are centered on an axis as the references point for zero. The vertical displacement of each stream is proportional to the value of that stream that is being represented. The x-axis of a stream graph represents time with the far left being the initial time and the far right being the final time. The differing colors is used mainly to distinguish the streams from each other. Stream graphs are best used for large data sets with a lot of categories to help distinguish overall trends or patterns. There are some downsides to stream graphs. The legibility of the graphs can be low if there are a lot of data groups in one area. Some smaller data groups may also be consumed by the larger data sets. Finally, there is no way to know the actual quantitative value of each data set as there is no numerical y-axis.

Histograms visualize the distribution of data over time intervals. Each bar represents the frequency of the data within that time interval, or bin. These types of graphs are best used to identify concentrations of data, extremes, and any gaps that may occur. These graphs are also useful for determining the more likely outcomes. A downside of this type of data visualization is it does not show the exact quantitative data. However, this downside is outweighed by how useful this graph is for analyzing trends of frequency.

A candlestick chart is generally used to show variation in price over time. Each candlestick shows the variation in price or some other variable in a smaller time period, and then the candlesticks together show variation over a longer time period. Each candlestick shows 4 main data points. The open price is the starting price of the period covered by the candlestick. The close price is the price of the product at the end of the period covered by the candlestick. The open and close prices are the ends of the real body, which is the rectangular part of the candlestick. The two lines extending from the rectangle are the upper and lower shadows. The shadows represent the highest and lowest prices of the time period for the candlestick that are above and below the open and close price. The color of the candlestick shows if the price increased or decreased. If the close price is lower than the open price, then the color of the candlestick is usually red or black. If the close price is higher than the open price, then the color of the candlestick is usually green or white. The best use of this type of data visualization is to see the overall trend of a price over a period of time.