Devin Eldreth
UNC Asheville
devin.eldreth@gmail.com
The fields of weather and climate are full of time-series data. Observations, model output, forecasts --- almost all aspects of weather and climate involve time dependent data that is often presented in the form of a graph. With this in mind, and considering that the scientific community and the world at large has been turning to the web for several years now as a primary means of communication, there are surprisingly few good tools and techniques available for presenting time-series data on the web. The most common solution is to use a desktop tool such as Microsoft Excel or Matlab to create a graph which is saved as an image and then included in a web page like any other image. Although this is straightforward and simple, it limits the user to one particular view of the data, disconnects the graph from the data in a way that makes updating a graph with new data an often cumbersome manual process, and does not provide the reader with the ability to combine and compare data from separate sources.
This situation is somewhat analogous to the state of mapping before the advent of GIS. Maps existed only in printed form, and creating a map was a laborious process. There were many disparate sources of maps, and information from separate maps could only be combined manually by creating a new map. In the last several years, however, the world of mapping has experienced a revolution in the form of web-based and other interactive computer technologies, to the point that it is now commonplace, for example, for everyone from small children to grandparents to easily browse through gigabytes of geographic data to locate an aerial view of their house or neighborhood, or create and print a customized trip map complete with driving directions and time estimates.
Multigraph is a software tool that seeks to bring a similar ease of presentation and viewing to time series data. Multigraph displays interactive time-series data graphs in web pages that includes a simple way of configuring the appearance of the graph and the data to be included. It allows multiple data sources to be combined into a single graph, and allows the user to explore the data interactively. Multigraph lets users explore and visualize "data space" in the same way that interactive mapping applications such as Google Maps facilitate exploring and visualizing geography.
Viewing a Multigraph graph is very simple and intuitive, and requires almost no instructions. Creating a new graph for inclusion in a web page involves writing a simple configuration file, and requires no programming. Multigraph is an Adobe Flash application and runs in any web browser that has Flash installed, which includes almost all browsers in Windows, Mac OS, and Linux. Multigraph can read data in a variety of formats, and can display data from a web service, allowing users to "surf" through large datasets, downloading only those the parts of the data that are needed for display.
Multigraph was created at UNC-Asheville's National Environmental Modeling and Analysis Center and NOAA's National Climatic Data Center (NCDC), and is freely available as open source software. This paper gives an introduction to viewing and creating graphs with Multigraph.