{"id":120471,"date":"2008-04-24T22:58:00","date_gmt":"2008-04-24T22:58:00","guid":{"rendered":"http:\/\/www.esri.com\/arcgis-blog\/products\/product\/uncategorized\/dot-density-mapping-with-arcmap-part-1\/"},"modified":"2008-04-24T22:58:00","modified_gmt":"2008-04-24T22:58:00","slug":"dot-density-mapping-with-arcmap-part-1","status":"publish","type":"blog","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/product\/mapping\/dot-density-mapping-with-arcmap-part-1","title":{"rendered":"Dot Density Mapping with ArcMap: Part 1"},"author":4391,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"open","ping_status":"closed","template":"","format":"standard","meta":{"_acf_changed":false,"_searchwp_excluded":""},"categories":[22941],"tags":[23191,31301],"industry":[],"product":[],"class_list":["post-120471","blog","type-blog","status-publish","format-standard","hentry","category-mapping","tag-cartographic-concepts","tag-symbology"],"acf":{"short_description":"By Alex Quitero and Daniel Smith, University of Redlands, Masters of Science in GIS Program\n\n\n\nSeveral weeks ago, after a colloquium give...","flexible_content":[{"acf_fc_layout":"content","content":"

By Alex Quitero and Daniel Smith, University of Redlands, Masters of Science in GIS Program<\/strong><\/p>\n

\"\"<\/p>\n

Several weeks ago, after a colloquium given by Dr. Aileen Buckley on the devolution of\u00a0cartographic theory<\/a>, we approached her about research opportunities that she mentioned. She was glad to accept our help and put us in contact with Dr. A. Jon Kimerling from the Oregon\u00a0State University. The research he was undertaking during his sabbatical in Redlands, CA dealt with a particular mapping method in the cartographer’s bag of tricks – dot density mapping. After discussing the research issues with Dr. Kimerling, we were tasked with developing a series of maps to supplement his research (see his presentation: “Dotting the Dot Map, Revisited<\/a>” and to document the workflow for creating dot density maps with ArcMap. This seemed to be easy enough and in fact was\u00a0quite easy given ArcGIS provides the tools necessary for completing this task.<\/p>\n

Here are the basic steps needed to create a dot density map.<\/p>\n

The first thing that is necessary\u00a0is areal data. For population dot density maps, census data are a good bet.<\/p>\n

Identify of the attribute that contains values for each\u00a0areal unit that you want to map.<\/p>\n

Once you have identified the data and\u00a0attribute to be mapped you need to define the dot size and dot unit value.\u00a0There are a few ways to do this. You can refer to the Mackay nomograph (slide 6 of “Dotting the Dot Map, Revisited<\/a>“) that has\u00a0been used for years or refer to Dr. Kimerling’s work\u00a0using probability theory to\u00a0define an optimal dot density from which the dot unit value can be determined (appears later in the same presentation).<\/p>\n

Now comes the ArcMap part. Right-click on your areal unit data in the\u00a0table of contents and select Properties. Select Symbology tab and on\u00a0the left hand side of the dialog box select Quantities (see below). The drop down box shows\u00a0several options, among them Dot Density. Select this option. You will see the\u00a0display change, and it will give you options for identifying the attribute(s)\u00a0to be mapped, dot value and dot size. Set these parameters to what you would like and visually inspect the dot density preview. Pay special attention to the\u00a0“Max” (maximum) preview box. Try to adjust your values, so that in the Max\u00a0preview the dots begin to coalesce. Click OK and ArcMap will draw the\u00a0appropriate number of dots according to the dot unit value in a random pattern,\u00a0giving you a dot density map.<\/p>\n

\"Density<\/p>\n

This dot density mapping is great, right? In many cases\u00a0where features are distributed evenly across your areal units this simple\u00a0procedure will work well, but what if we want a more realistic depiction of\u00a0where dots should be placed? ArcMap has the functionality to handle this more complex\u00a0situation in the form of applying masking to the layer and eliminating unsuitable areas for dot placement. The process for applying a mask is as simple as\u00a0creating the dot density map, as explained above, but there are additional\u00a0considerations. The first is defining exclusion or inclusion areas.<\/p>\n