EPA Science Inventory

Linked Micromaps: Statistical Summaries of Monitoring Data in a Spatial Context

Citation:

McManus, M., Q. Payton, M. Weber, T. Kincaid, AND T. Olsen. Linked Micromaps: Statistical Summaries of Monitoring Data in a Spatial Context. Presented at 9th National Monitoring Conference, Cincinnati, OH, April 28 - May 02, 2014.

Description:

Communicating summaries of spatial data to decision makers and the public are challenging. Linked micromap plots (LMplots) provide a way to simultaneously summarize and display both statistical and geographic distributions of data from surveys such as the National Aquatic Resource Surveys (NARS). The production of LMplots to display statistical summaries associated with areal units or polygons, such as watersheds or ecoregions, can be cumbersome. We identify four steps that streamline the process for making LMplots and incorporate those steps in the R package micromap. Those steps include: smoothing complex boundaries of polygons to just convey regional identity and neighbor relationships, linking the spatial and statistical data, making a draft LMplot, and refining that plot. As an example we make an LMplot summarizing pH data over nine regions from the National Lakes Assessment, with that display showing interquartile ranges and confidences limits. Being able to incorporate such measures of variation is an advantage LMplots have over pin or choropleth maps. For an example of exploratory spatial data analysis, we make an LMplot using stream conductivity and condition from a spatially balanced probabilistic survey of streams in West Virginia to identify local and global outliers. LMplots can also be applied to statistical summaries for administrative units, such as counties, states, or countries, and have been used with public health, demographics, and agricultural data. The ability for viewers to discern both statistical and spatial patterns is a strength of these plots, and we hope that visualizing georeferenced statistics in this manner will become more common. The views in this abstract are those of the authors and do not necessarily represent the views or policies of the U.S. EPA.

Purpose/Objective:

This presentation, "Linked Micromaps: Statistical Summaries of Monitoring Data in a Spatial Context", is to inform participants at the 9th National Monitoring Conference on a way to communicate summaries of spatial data to decision makers and the public. Linked micromaps provide a way to simultaneously present geographic context and statistical summaries of data. Monitoring data collected over areal units, such as watersheds or ecoregions, can be displayed as micromaps in documents, such as intergrated water quality monitoring and assessment reports.

URLs/Downloads:

MCMANUS_MONITORINGCONFERENCE_MICROMAP.PPTX

Record Details:

Record Type: DOCUMENT (PRESENTATION/SLIDE)
Completion Date: 04/02/2014
Record Last Revised: 04/02/2014
Record Created: 04/02/2014
Record Released: 04/02/2014
OMB Category: Other
Record ID: 272396

Organization:

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF RESEARCH AND DEVELOPMENT

NATIONAL CENTER FOR ENVIRONMENTAL ASSESSMENT