Disease Mapping with an Online Prevention Atlas

The National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention Atlas was created to provide an interactive platform for accessing data collected by the USA Centers for Disease Control (CDC) Prevention (NCHHSTP).  This interactive tool provides CDC an effective way to disseminate data, while allowing users to observe trends and patterns by creating detailed reports, maps, and other graphics.

I find the Atlas, which is based on Esri technology, quite useful and quick to draw.  Its integration of its maps and graphs makes the data easy to understand.  For integrating the data into a GIS environment, the site provides an export to Excel capability.  The resulting Excel files only need a light edit before importing to GIS.  The only drawbacks are that this atlas only focuses on the diseases mentioned above, and it only contains data for the USA, on a national and state level.  However, with the continued expansion of GIS in health, the number of GIS-compatible data sets and data portals increases monthly, and these portals can fill the above-mentioned gaps.

NCHHSTP Disease Atlas

Covering Our Tracks

In our not-so-distant, non-digital past, good guys pursued bad guys with the aid of a faithful hound or trusty local guide. The trail of said bad guys could always be followed from the footprints they left or the vegetation they displaced, subtle impressions in the natural environment that lingered for a short while before they were erased by wind, rain or the occasional foraging coyote.

Nowadays, those of us who never leave home without our mobile or cell phone, leave a potentially more sinister and permanent record of our travels.

James Ball and Craig Timberg recently wrote an article for the Washington Post about the ongoing legal debate in the USA about the use of GPS data in criminal cases (GPS technology finding its way into court). In two unrelated cases, cellphone location data were used to help secure arrests, and the use of that data was sanctioned by the courts. The individuals involved did not have a “…reasonable expectation of privacy” when it came to their cell phone data and it could be collected, without a search warrant. Fearing the potential for abuse as increasingly sophisticated tracking technologies become available, legal challenges to use cell phone location data in this manner were immediately launched. The debate looks set to make it all the way to the Supreme Court.

It’s not just GPS-enabled phones that are involved. Phones without GPS devices, and their owners, can be tracked as they move between signal towers. How many phone users are aware of this and how many know who collects and has access to that information? If we knew more, would we modify our cell phone usage or would we trust the data collectors not to abuse our private location information?

USGS LandsatLook Resource for Viewing and Downloading Landsat Satellite Imagery

I have been experimenting the US Geological Survey’s new LandsatLook resource to view and download Landsat ETM and TM images, and am finding it easier to use than other Landsat portals.  The process of selecting scenes using the Esri basemap, and then narrowing the query by date, cloud cover, and image quality is quite straightforward.  In particular, the ability to display the Landsat footprints against the Esri basemap is a huge leap forward over other portals in the responsiveness of the site and its usability.  As we discuss in our book, an ongoing desire of the GIS community is to reduce the amount of time acquiring data, and this resource meets that criterion nicely.

In addition, for those data users who do not want to download the scenes, but to view them against a variety of basemaps, “natural color” jpg images have been derived from the ETM, TM, and MSS images in the archive for the globe.  There is also a thermal image derived from TM Band 6 and ETM band 61-high gain.

LandsatLook Interface

All of these derived images as well as the original imagery can be viewed online or downloaded.  And even the derived images are georeferenced with the necessary files that enable them to be easily read by GIS software.  Once you select the scenes you need, you add them to your cart, and then Get Your Data, after logging into the service, making the whole process almost as easy as ordering from, say, Amazon or any online store.  And best of all, everything is free.  Because this resource provides the ability to view the images online, the resource makes an excellent research and teaching tool, opening up this treasure of imagery to the non-GIS analyst.

Update February 2021:

I found this tool very useful some years back, but after revisiting it this month, I cannot recommend it these days.  It is slow to load and find imagery.  When I finally did get a list of images in the viewer, as shown below,, I was greeted with a “drawing” message and the page automatically refreshed every 20 seconds and was almost unusable.  If your experience differs from mine, I would love to hear about it.  Fortunately many other good Landsat portals exist nowadays; see our list here:  https://spatialreserves.wordpress.com/2019/08/04/the-top-10-landsat-image-sites/ 

—Joseph Kerski 

 

Cartographic vs. Geographic

Map generalisation is a compromise between visual clarity and resolving the conflict of displaying map features at smaller scales. Ideally the process would be fully automated, with rigorous algorithms and techniques for feature simplification; in practice, the end result is often the interpretation of an individual cartographer.

In the GIS Guide to Public Domain Data we make the point that many digital maps are often no more accurate than the original source paper documents that were compiled in a time when legibility was often deemed more important than spatial accuracy. Generalisation was more of a manual craft than scientific process, with features offset from their true location for impact. Although this cartographic interpretation persisted into the corresponding digital version of the map, the accompanying metadata rarely, if ever, described the original source and production techniques.

Even if it were documented in the metadata, how many people would pay much attention and consider alternative digital data products instead? If it’s available on the internet, in a format I want and it looks good, that makes it OK – correct?

A plethora of digital spatial data products are now available, and easily accessible, in the public domain, but bear in mind a good cartographic product may not necessarily be a good geographic product.