ArcGIS » Don Boyes

I was skimming through my Twitter stream this morning and came across a tweet from the intrepid Michael Gould (@michael_d_gould) mentioning David J. Unwin’s digital workbook “Numbers aren’t nasty: a workbook of spatial concepts“. I’m a big fan of David Unwin’s Geographic Information Analysis (co-authored with David O’Sullivan), so I downloaded the workbook (it’s free) and the accompanying data sets. I was intrigued to see that this included coordinate data for John Snow‘s map of cholera deaths. Virtually every GIS student learns about the pioneering epidemiological work John Snow did using spatial analysis of cholera deaths, tracing them to the infamous Broad Street pump. I thought I would be clever and quickly map them using Google Fusion Tables. What I soon realized was that the coordinates were created using an arbitrary system that placed them somewhere in Africa and, as is often the case, realized that I needed to slow down, take a closer look at the data and what I was doing, and see what was going on.

First, I did some quick online searching, and was surprised that I wasn’t able to find a georeferenced version of the data. So I went back to the data at hand. In Unwin’s workbook, he states that the points were originally “digitized at the request of Professor Waldo Tobler (UCSB) by Rusty Dodson of the US National Center for Geographic Information Analysis from a reprint of Snow’s book On Cholera (Oxford University Press, London)”. Since the original data had an arbitrary coordinate system, I used ArcGIS 10 to georeference an image of the map using the Bing Maps hybrid base map, and then spatially adjusted the points (both deaths and pump locations) to match the image. I then used the ArcGIS Online topographic base map to create the following figure:

Locations of water pumps and cholera deaths from John Snow's map (the Broad Street pump is the blue symbol at the center of the map)

As this is based on a sketch map scanned from a book, all locations should be treated as approximate.

I must admit that I have sometimes neglected to mention John Snow and his work in my introductory GIS course (for shame!), so now I have some actual GIS data and a modern map to show in class. It may also turn into a good opportunity to introduce web mapping as well. After I saw Michael Gould’s original tweet, he and I discussed how we had both been meaning to find the replica Broad Street pump in London (tip: the street is now called Broadwick). Naturally, Mike tweeted a link to an ArcGIS Explorer map of pump locations which of course inspired me to put my version of the pump and death locations on there as well:

View Larger Map

I hadn’t used ArcGIS Explorer much, and intend to incorporate it into my courses, so this was a good excuse to try it out. Once I got it on the web, I did another search and found that someone else had already put a similar version online – oh well! At least I learned a lot by going through this exercise, and what else was I going to do on a Friday afternoon?

I should also mention that I came across a simple but very interesting example of spatial analysis of the data done by what appears to be a student named John Mack. His web page inspired me to start fooling around with the kernel density tool, and I came up with a quick example:

Density of cholera deaths from John Snow's map

Density of cholera deaths using a 100 m kernel density function

I will be the first to say I made this as a quick example, and would not put too much faith in it. However, I may spend more time on this later, as it might be a good data set for illustrating density analysis.

So, there you have it. Out of one tweet I read this morning came an entire day’s activity and some data and figures I can use in one of my GIS courses. Twitter can eat up a lot of time, but sometimes I come across little gems that can be really interesting and useful.

Update: I have created a map data layer package of the pump and death locations that can be downloaded from ArcGIS.com.

Update: I have created zipped shapefile and KML versions of the files as well, both in GCS (WGS84). In both versions, there are three files: one file contains one point location of the Broad Street Pump, one files includes all of the pumps in the original map (including the Broad Street pump) and one file contains the cholera deaths recorded on the map.

I am currently in the process of re-evaluating my PowerPoint slide designs and templates that I use for my lectures. As a rough estimate, I have somewhere between 2,000 and 3,000 slides spread over many files. Over the last ten years, I have used the same template for all of them, with minor modifications. In the next few months, I plan to give them an overhaul – update the designs and screenshots (there are still some Windows XP slides lurking in some of my files, which really stick out now, and not in a good way), experiment with new layouts, graphics, and content. I have just bought some books that I’m sure will be very helpful in this process, including Slide:ology by Nancy Duarte, Presentation Zen and Presentation Zen Design by Garr Reynolds, and the Non-Designer’s Presentation Book by Robin Williams. I like to think I’m fairly good at slide design and presentation, but I also know there is much more I can learn. Some of what they recommend is old hat to me (e.g., less text, more graphics) or cliché (the expression “death by PowerPoint” is so overused but, sadly, still often needed) but I am voraciously reading all of these books to broaden my thinking for presentation design and execution.

So, on the topic of slide design, I thought I would share a couple of tips that might be helpful when using ArcGIS maps in PowerPoint. First, I design maps specifically for use as slides whenever possible. If you have the time, your audience will notice the difference (the small fonts and pastel shades often used for print maps just don’t translate well when projected for any kind of larger audience). In ArcMap, create a custom page size that matches the dimensions you want to use, such as 7.5 x 10 inches for a map that will fill a traditional slide (sometimes I make them 6×10 inches to leave room at the top for a title). Then set the data frame size to be the same as the page, with no offset or margin.

: Custom ArcMap page layout for PowerPoint. Here my map will be 6 inches high to leave room for a title above.

Create your map, keeping in mind that the colour schemes, line weights, and symbol sizes should be slightly exaggerated. I tend to use somewhat brighter, more vibrant colours for PowerPoint than I would for a print map, especially if the room I will present in won’t be that dark. You also want the message you are communicating with your map to be easily grasped in a few seconds (this may also be true for print, but I think more so for presentation). I then export the map from ArcMap as a 200 dpi jpeg file. If 200 dpi seems like overkill, it often is, but it gives me more flexibility if I later want to enlarge and crop the map. The trade-off in file size is worth it for me, but you may want to go with a smaller image resolution. I then add the map into PowerPoint. I usually cut and paste the legend from ArcMap directly into PowerPoint so I have the option of moving it later if I want to add a label or other text to the map.

When adding attribute tables to PowerPoint, follow the same guidelines for text size you would use for any other slide text. In other words, the attribute table text should be BIG. I often see presentations where people fail to do this and I always think “Why show an attribute table if we can’t see the contents?”

: ArcMap attribute table with large type size

When bringing in screenshots of attribute tables or any dialog box into PowerPoint, I first set the size of the window so that I have a predictable, consistent size for every one. There is an incredibly useful, free utility for Windows called Sizer (http://www.brianapps.net/sizer/), that allows you to set custom window sizes (it does not officially support 64-bit Windows 7, but I have not had any issues). Since I show a lot of tables and dialog boxes in my lectures, I find it helpful to maintain consistent sizes throughout.

: Sizer dialog box for setting custom window sizes.

As time-consuming as slide design can be, I really enjoy the process, as I’m always trying to find a simpler, more effective way to tell a story. I hope the above tips will help streamline your workflow and help you do the same.

Don Boyes

John Snow and serendipity

Using ArcGIS maps and tables in PowerPoint