This heat map shows changes in frequency of climate- and energy-related terms (e.g. “climate change”) in a selection of five EPA document collections: issues of EPA Journal, EPA news releases, EPA strategic plan documents, EPA budget summaries, and EPA budget justification documents. The blue bars at the top indicate the time span of each document set. At the top a timeline shows key events related to the history of the EPA and climate change science. Hovering over a marker in the timeline displays information about the key event.
The color of each cell represents the normalized frequency of the term for the given year, i.e., the number of times the term appears in the selected document groups divided by the number of pages of documents published in that year. Each term on the left side of the visualization represents clusters of related phrases grouped together to compute the frequency of the term across the documents. For example, the frequency of the term “climate change” includes the combined frequency of “climate change,” “climatic change,” and “changing climate.” These groupings help us capture variations in terms that have the same basic meaning.
To see the words included in each term group, hover over the heading for the term group in the left column. When you hover over an individual cell in the heatmap, a tooltip displays the term and normalized frequency of that term for the given year. To toggle document sets on or off, click on the corresponding header label for the given document set. The visualization automatically updates to display new counts when document sets are toggled.
Steven Geofrey, Leif Fredrickson and Shannan Lenke Stoll, "Climate and Energy Terms Over Time in EPA Documents," A People's EPA.