What is a Change Matrix?
No it’s not something from the movie involving Neo or computers using humans as their energy source. Although at first glance it can be just as confusing. A change matrix is a table, similar to a spreadsheet that quantifies the amount of change that occurs between two dates of land cover. It can be used to analyze the multitude of potential land cover change combinations that may occur between two time periods. For example, the Coastal Change Analysis Program (C-CAP) maps a potential of 25 land cover classes per time period, which could result in 625 (25 x 25) possible change classes between two dates.
A typical change matrix will be set-up with one date of land cover down the left edge, and a second date of land cover across the top. The number of rows and columns is determined by the number of classes in the land cover image. If you were interested in a specific land cover change, you would intersect the row from Time 1 and the column from Time 2 representing that change. The resulting cell would indicate the amount of change.
In the above simplified matrix, the user can see that between Time 1 and Time 2 there were a total of 34 square miles of new Development (red cells); 15 from Agriculture, 17 from Forest, and 2 from Wetlands) Yellow cells indicate areas of no land cover change.
In addition to determining net changes in land cover over time, a change matrix can be used to identify offsetting losses and gains in land cover. In the above example, there was a net loss of 3 square miles of Agriculture (120 to 117). More detailed analysis shows that there was a loss of 20 square miles of Agriculture (15 to Developed and 5 to Forest) and a 17 square mile gain of Agriculture (12 from Forest and 5 from Wetland). Examining offsetting losses and gains can give a more complete picture of the change taking place, which may have implications to the quality of the area (forest and wetland for instance).
Creating a change matrix can be a daunting task as well but, lucky for you, we have already performed the heavy lifting for C-CAP land cover change. State based bivariate, or land cover change, files can be downloaded here. These files contain the potential 625 land cover change values mentioned earlier. Once you have the raw data, you can download our custom spreadsheet which will not only build a change matrix, it will provide you with sample graphs and tables detailing change for your area (note, this spreadsheet was custom built to work with C-CAP land cover change only). For more detailed reporting and visualizing of change information, please visit the C-CAP Land Cover Atlas.
If you have other land cover data sets and would like to create similar change files and matrices, please feel free to contact us for more support.