Last night at the Barry/Lawrence ARES meeting in Monett, I told people about the SEMA Disaster Support Mapbooks, a set of 1:25000 Missouri atlases, one atlas per county, using the US National Grid (USNG) Coordinate Reference System (CRS), in a Geospatial PDF format (readable by most PDF viewers with some applications providing more features than others). This post includes the link to those map resources, explains them a bit more fully, and lists some other free or open catrographic resources I have found for Missouri emergency response and data analysis. There is a page on the LCSA site to list Missouri mapping resources, and that page will grow over time.
The SEMA Disaster Support Mapbooks is an important project, not just because it provides high quality digital/printable maps with both vector and raster (satellite imagery) layers, but also because
- it uses a standard coordinate reference system which all MO emergency response efforts can and should use: the US National Grid, functionally identical to the Military Grid Reference System (MGRS) grid many GPS systems support , and
- it showcases an ability to provide complex maps with multuiple layers and embedded data in an single package which is
- easy-to-distribute,
- easy-to-print,
- easy-to-use, and
- easy to mark up and pass along.
As a total, these features make the maps nearly ideal for 90% of emergency response purposes.
What is the US National Grid?
The National Grid is Coordinate Reference System using a Universal Transverse Mercator (UTM) projection on top of the WGS-84 datum. For non-map geeks, this means that the map preserves angles and directions for navigation (the top of the map is north),which is why Mercator projections have been the choice of sailors for centuries. A "projection" is how one makes convenient flat maps from the Earth which is very stubbornly not flat. WGS-84 is a "spheroid", a model of the earth taking into account the various bumps and oddities which make it not a perfect sphere.
Given that the Earth is not flat, projects always result in some distortion: either distances or angles or areas on paper are not true to real life. If you look at a Mercator projection of the Earth, you see that Africa, which is larger than North America appears no bigger and that the arctic regons are stretched to the point of ridiculousness. The Universal Transverse Mercator solves this issue by dividing the planet into grid regions and tweaking the projection to minimize distortion in each region: thus the US National Grid, the Australian National Grid, the British National Grid, and so forth, each section of the map showing its region in the best possible manner. The grid is actually divided into 100,000 meter squares with a number and letter designation. Lawrence County, MO, ends up in grid 15S. Locations in the 100,000 m grid are easily identified as a Northing and Easting: the number of meters from the bottom left of the grid square and distances between two points in the grid are then... well... just distances you can figure given any High School Geometry class. Distances between points in different grids take a bit more work but will rarely come up in our relief efforts. Even if you are not a map geek, it is worthwhile to familiarize yourself with a few of the concepts relating to projections, specifically with the trade-offs between the UTM approach, the Public Land Survey System which was used to survey Missouri (what our roads, addresses, and sections are based on), and the older US Geographic Survey (USGS) maps ("quads") which used a polyconic projection and are still the basis for a lot of common road atlases.
The Military Grid Reference System (MGRS) used by the US DOD (and underlying GPS) is also a UTM grid system based on WGS-84, and is therefore functionally identical to the USNG coordinate system. Since many common GPS/APRS devices and applications will return MGRS grid numbers, those grid numbers can be used on USNG maps. This may or may not always be true (if they are not kept up to date with each other), but probably will be for at least the next few years and will likely always give close results.
The SEMA download page contains a link to a powerpoint presentation and some sample maps which show you how the USNG grid system works, how to find a point from a grid reference, how to determine the grid reference for a point, and has a printable business-card sized graticule (little ruler) for working with USNG maps at common scales.
What is a Geospatial PDF?
A Geospatial PDF (Terrago Trademark: GeoPDF) is a PDF with multiple layers, at least some of which represent maps or images tied to a precised geographic location. In other words, the PDF is aware of the relationship between points in the map or image and points in the real world (and one can therefore plot and measure distances inside the PDF). Furthermore, features on the map can be tied to further information or metadata about the real-world features; a river can be tied to information about its name, seasonal boundaries, flow rate, and so forth. A point representing a historical tornado touch down can be tied to its force-rating, width, length of track, damage, and casualties. A road can contain information about is construction and materials.
Tying this information together is not new. Applications called Geographical Information Systems have been doing this since the 1950's. What is new is bundling all of the information into a nice, neat package which some else can view and manipulate easily without having special software themselves. Most of the features needed were already supported by PDFs, and those which features which were not already there have been submitted as an international standard (ANSI/ISO 32000) which PDF readers starting with Adobe Acrobat 9 are now beginning to 'widely support. Someone with complex GIS software and the appropriate training can produce a Geospatial PDF and someone else with no special software and minimal training can open it, find the information they need, and even make notes on it to distribute to others ("This is where the Incident Command Center is. This is where the Staging Area is. The danger zone covers the marked area").
The SEMA Disaster Support Mapbooks can be read in any PDF reader and printed on 8.5x11" mapsheets (I have tried them specifically in Adobe Acrobat, in several Linux applications, including "Document Viewer" and "GwenView"; they load fine in Acrobat Reader on an Android Smartphone, but there is only so much you can do with them on a little handset...). These particular PDFs can only be marked up (annotations, drawing lines and boxes, etc.) on full-fledged Adobe Acrobat (Reader will only view and print them). GwenView on Linux will also mark them up. There is an index map in each county atlas which will allow you to click on and load the mapsheet you wish and they are marked with the boundaries of the standard USGS quads so you can refer to older paper map atlases. Most of these viewers let you see and select the map layers, to turn on or off display of satellite images or topographic contours, for instance, and allowing you, therefore, to see or print only the details you need to suit your specific purposes. A freely downloadable toolbar from TerraGo ("Terrago Toolbar") will install on Windows Acrobat to let you do some fairly complex manipulations, such as calculating perimiters or areas.
The Maps, for all of their detail, are reasonably compact. Lawrence and Barry County will fit (barely) on a single CD. Therefore, it is straight-forward to distribute digital map books to every organization and volunteer who may need them in the field, ensuring that everyone is, quite literally, on the same page.
In a future article, I intend to cover the free Quantum GIS map viewing/editing program which will allow us to do some sophisticated things with maps, but it is enough for the moment to know that good maps are available for Missouri operations and easy to use.