- Heat map
A heat map is a graphical representation of data where the values taken by a
variable in a two-dimensional map are represented as colors. A very similar presentation form is aTree map .History
Heat Maps originated in 2D displays of the values in a data matrix. Larger values were represented by small dark gray or black squares (pixels) and smaller values by lighter squares. Sneath (1957) displayed the results of a
cluster analysis by permuting the rows and the columns of a matrix to place similar values near each other according to the clustering.Jacques Bertin used a similar representation to display data that conformed to aGuttman scale .The idea for joining cluster trees to the rows and columns of the data matrix originated with Robert Ling in 1973. Ling used overstruck printer characters to represent different shades of gray, one character-width per pixel. Leland Wilkinson developed the first computer program in 1994 (SYSTAT ) to produce a cluster heatmap as a high-resolution color graphic. The Eisen et al. display shown in the figure is a replication of the earlier SYSTAT design.Web Heat Maps
Heat maps have been used for displaying areas of a Web page most frequently scanned by visitors. These have been incorporated in Web analysis tools such as Google
AdSense .Biology Heat Maps
Heat maps are typically used in
Molecular Biology to represent the level of expression of many genes across a number of comparable samples (e.g. cells in different states, samples from different patients) as they are obtained fromDNA microarrays .Tree Maps
The
Treemap is a 2D hierarchical partitioning of data that visually resembles a heat map. They have been most famously used in the "Map of the Market" applet featured onSmartMoney 's website.Mosaic Plots
A mosaic plot is a tiled heat map for representing a two-way or higher-way table of data. As with treemaps, the rectangular regions in a mosaic plot are hierarchically organized. The means that the regions are rectangles instead of squares. Friendly (1994) surveys the history and usage of this graph.
References
*cite book | author=Bertin, J. | title=Sémiologie Graphique. Les diagrammes, les réseaux, les cartes | year=1967 |publisher=Gauthier-Villars
*cite journal | author=Eisen, M.B., Spellman, P.T., Brown, P.O. & Botstein, D. | title=Cluster analysis and display of genome-wide expression patterns | journal=Proc. Natl. Acad. Sci. USA | year=1998 | volume=95 | issue=25 | pages=14863–14868 | url=http://www.pnas.org/cgi/content/full/95/25/14863 | doi=10.1073/pnas.95.25.14863 PMID 9843981 doi|10.1073/pnas.95.25.14863
*cite journal | author = Friendly, M. | title=Mosaic displays for multi-way contingency tables | journal= Journal of the American Statistical Association | year=1994 | volume=89 | pages= 190-200 | url=http://www.math.yorku.ca/SCS/Papers/drew
*cite journal | author = Ling, R.F. | title=A computer generated aid for cluster analysis | journal=Communications of the ACM | year = 1973 | volume=16 | pages=355–361
*cite journal | author=Sneath, P.H.A. | title=The application of computers to taxonomy | journal=Journal of General Microbiology | year=1957 | volume=17 | pages=201–226
*cite book | author=Wilkinson, L. | title=Advanced Applications: Systat for DOS Version 6 | year=1994 |publisher=SYSTAT Inc. |id= ISBN 9780134472850External links
* [http://quotes.nasdaq.com/screening/heatmaps.stm NASDAQ Heat Maps] , an example of heat maps applied to stock market data.
* [http://bioinformatics.ubc.ca/matrix2png/ Matrix2png] , a tool for creating heat maps from data in text files. It can be downloaded and run, or used through a web interface
* [http://www.mbeckler.org/heatMap/ Java HeatMap] , a Java class to draw a heat map from a rectangular array of data. It is open source and can be easily included in your own application.
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