What does double digitized polygon mean?

Decoding “Double Digitized Polygon”: A More Human Look at GIS Jargon

Okay, so you’re diving into the world of Geographic Information Systems (GIS), huh? It’s a fascinating place, but let’s be honest, it’s also full of jargon that can make your head spin. One of those terms that might pop up is “double digitized polygon.” Sounds complicated, right? Well, it’s not as scary as it seems. Let’s break it down in plain English.

First off, why should you even care? In GIS, getting things right matters. Precision is key. So, when you hear a term like “double digitized polygon,” it’s flagging a potential issue that could mess with your data.

So, what’s digitizing all about anyway? Think of it like tracing. Imagine you have an old paper map, and you want to get that information into your computer. Digitizing is the process of taking those real-world features – buildings, rivers, property lines – and turning them into digital objects that your GIS software can understand. You’re essentially drawing lines around them and giving them coordinates.

Now, here’s where the “double” part comes in. A “double digitized polygon” basically means that you’ve got some duplicated effort going on, or, worse, a potential error lurking in your data.

There are a couple of ways this can happen. The most common is when you have adjacent polygons – think of neighboring property parcels. If you’re not careful, you might end up digitizing the shared boundary between them twice – once for each parcel. It’s like drawing the same fence line twice, once from each yard. Because polygons are stored as rings, the first and last coordinates are the same. This means that the coordinates defining the border between two adjacent polygons are essentially duplicated in the dataset.

Another way it happens is just plain old accidental redigitization. Maybe you weren’t paying attention, or the data management wasn’t up to par, and you ended up digitizing the same polygon a second time, completely unintentionally. I’ve seen it happen more times than I care to admit!

Why does this happen? Well, a few things can contribute. Back in the day, when everything was manual, it was super easy to make this mistake. You’re sitting there with your digitizing tablet, tracing lines, and without the right tools or procedures, bam! Double digitization.

Also, some older GIS formats aren’t very smart about this. They don’t have built-in rules to prevent overlaps or gaps. It’s like they’re saying, “Hey, go ahead and draw the same line twice if you want!”

And sometimes, it’s just the software or the workflow you’re using. If it doesn’t have good tools for handling shared boundaries, you’re more likely to run into this problem.

So, what’s the big deal? Why should you care if you have a few double digitized polygons? Well, it can cause a surprising number of headaches.

First, it bloats your data. All that duplicated information takes up extra storage space. Second, it can lead to topological errors – overlaps, gaps, all sorts of weirdness. And that can really mess with your analysis. Imagine trying to calculate the area of a forest, and you’re double-counting some of the trees along the edge. Your numbers are going to be way off!

Plus, cleaning up these errors is a pain. It can take hours of manual editing or require specialized tools. Trust me, you don’t want to go there.

Okay, so how do you avoid this mess? Luckily, there are some pretty straightforward solutions.

The best approach is to use GIS formats that understand topology. These formats, like geodatabases, are smarter about spatial relationships. They can automatically prevent overlaps and gaps.

Also, learn to love snapping tools. These tools automatically connect lines and vertices when you’re digitizing, making sure that adjacent polygons share a common boundary. It’s like having a little helper that keeps you from drawing the same line twice. The “auto-complete polygon” tool can also be a lifesaver.

Some software even has tools specifically designed for this, like the “Difference Polygon” tool in ArcGIS Pro. It lets you create adjacent polygons without redigitizing the shared border.

Of course, good old-fashioned careful work habits are important, too. Train yourself and your team to be extra mindful of shared boundaries. A little attention to detail can save a lot of headaches down the road.

And finally, make sure you regularly validate and clean your data. Run checks to identify and correct any topological errors. Think of it like giving your data a regular checkup to keep it healthy.

In a nutshell, “double digitized polygon” is a fancy way of saying you might have some duplicated effort or errors in your GIS data. It’s a reminder that in the world of spatial data, precision matters. By understanding what it is, why it happens, and how to avoid it, you can keep your data clean, your analysis accurate, and your life a whole lot easier. Now, go forth and digitize responsibly!