In light of the recent noises coming out of North Korea, I wasn’t too surprised to see an article about their missile ranges. However, I was dismayed by the following infographic:
No, I’m not upset at the range of the missiles, I’m upset with how the cartographer drew them. What you see there is a Euclidean distance range, which only takes into account the Cartesian coordinates. The map should really look something like this:
- Notice how the first map vastly underestimates the portion of the globe the missiles could potentially reach. Why is there such a big difference? This is a result of how the globe is projected onto the flat map sheet. Trying to fit a sphere onto a flat surface inevitably introduces distortions of one sort or another. Because of this, the scale actually varies across the map. In this case, the scale gets larger with increasing latitude. The real problem arises when a mapmaker performs a simple Euclidean buffer, which is based off of map scale.
- While this works well enough for local analyses, trying to do the same thing over a larger area will produce incorrect results. When working at continental or global scales, you need to instead use a geodetic distance, which accounts for the true distance over the surface of the Earth. This looks really strange and wrong, but it makes sense when you realize the distortions introduced by projecting your globe will also apply to your distances.
- This is a great reminder of how you have to keep distortions in mind when reading, analyzing, or creating maps. It’s easy to just take the map at face value, but your conclusions are going to be incorrect if you use the map incorrectly. This is especially true when working with a map that covers large areas. Unfortunately, I see this kind of mistake pretty frequently. In fact, I recall seeing another incorrect map of the very same subject a few years ago, and someone wrote the same criticism. If anyone knows the link to that other map/criticism, please let me know in the comments. It’s too bad some mappers seem to not have learned their lesssons, but we should all take heed and make sure to make our maps carefully and use them wisely.
Ever been stuck at the airport and wondered just where your flight was anyway? Or maybe you wanted to know just how many planes were overhead? A friend shared this awesome site with me that displays live radar info on airline flights, showing you where they are in the world. It’s incredible to see just how many flights are in the air!
Look at them all!
In addition to being an informative visualization, if you click on a flight, a sidebar appears with details on the airline, the origin and destination, and position in three dimensions. Clicking on a flight also displays the flight track it has followed to this point. All this is great, but the real icing on the cake is the cockpit view. The website leverages Google Earth to simulate what the view from the cockpit might look like. It’s a bit silly, but how cool is that! Click and enjoy!!
In flow accumulation modeling, a common bit of data needed is the average upslope value of a parameter of interest, such as slope or curvature. In most cases, this is simply a matter of calculating a flow accumulation weighted by the parameter in question, then dividing this by the unweighted flow accumulation. But what if you want average upslope aspect? Since aspect is measured in degrees, and a value of 0° and 360° are the same, a simple arithmetic mean will be useless. So, what to do? In this post, I will walk you through the process of calculating the mean upslope aspect using ArcGIS, and leave you with a working python script that will automate the process.
Raw aspect raster, in ArcMap’s default Technicolor scheme.
As you may recall from my review of MAPCITE’s Excel Addin, I was having trouble with the polyline and poly shape features. Originally, I was going to just update the original post with the response from customer service, but their amazing turnaround time merits a full-fledged followup post. I had emailed customer service about my problem, and they responded the same day that they would forward it to the development team. The next morning, their was an email in my inbox informing me that they had fixed the bug with the software and tested it. I downloaded the new version and installed it, and I was able to make polygons and lines!
This week, I’ve taken MAPCITE’s Excel plugin for a quick test drive to see what it can do. I’m not getting any money, endorsements, or other compensation for this, so these are my own thoughts on the product. The software is easy to install and easy to use, and provides valuable added functionality to Excel. There were some limitations and a few stumbling blocks, but overall this is a useful product. Read on for the full report.
Looks like it’s always been there!
So, let’s say you need a map. And let’s say you don’t know much about this whole GIS thing. Wouldn’t it be nice if you could just take your spreadsheet of addresses or lat/long points and make a map, just like you would make a chart or graph? Well, the folks at ESRI, MAPCITE, and the LibreOffice Community all thought so, and have developed spreadsheet extensions to help you do just that. This has huge potential for spatially empowering the spreadsheet-enabled public, as well as reserving valuable GIS analyst time for more complex projects.
These extensions have a huge range in terms of number of capabilities and end-user cost (free to as much as you care to pay). Over the next few weeks, my mission is to compare these mapping extensions and see how they stack up. Which one is the “best”? What do you get for your money? Just how good of a map can you make with a spreadsheet, anyway? I’ll be exploring these questions, one extension at a time, and summarizing the results in a final post at the end. Stay tuned for review #1: MAPCITE’s Excel®™ Add-In.
Photo credit: Emma Rearick
Hello! I’m Jay Guarneri, a Master’s student at the School of Forest Resources. I’m currently studying landscaping modeling using Geographic Information Systems (GIS), but I maintain diverse interests such as marine biology, food & wine, and art. In the weeks and months to follow, you can expect to see musings on geography and cartography, how-to guides for GIS analyses in various software platforms, and announcements and reviews of new GIS software and developments.