Combining multiple DEMs into one file geodatabase

Wrangling DEMs: From Scattered Files to a Smooth Geodatabase

Digital Elevation Models, or DEMs, are the unsung heroes of GIS. They’re basically the digital equivalent of those cool 3D maps you might’ve seen as a kid, showing you the lay of the land. If you’re working with terrain data, you’re almost certainly using DEMs. Now, sometimes you’re lucky and have one nice, tidy DEM covering your whole project area. But more often than not, you end up with a bunch of DEM files, each covering a piece of the puzzle. That’s where combining them comes in, and putting them all into a single file geodatabase is like giving them a proper home. Trust me, it makes life so much easier.

DEMs and Geodatabases: A Quick Refresher

So, what exactly is a DEM? Think of it as a grid, where each square has a number representing the elevation at that spot. Simple, right? These grids are super useful for everything from figuring out where water will flow to creating realistic 3D visualizations.

Now, about file geodatabases. You might be thinking, “Why not just stick with shapefiles?” Well, shapefiles are like that old car you keep meaning to trade in. They get the job done, but they’re limited. File geodatabases, on the other hand, are like a shiny new SUV: they can handle way more data, offer better performance, and have all sorts of cool features. Storing your DEMs in a file geodatabase is like moving from a cramped apartment to a spacious house – everything’s just better organized.

The “Mosaic to New Raster” Magic Trick

Okay, let’s get down to the nitty-gritty. The key to combining DEMs is a tool called “Mosaic to New Raster.” It sounds intimidating, but it’s really not. It’s like taking a bunch of puzzle pieces and assembling them into a single, beautiful picture. Most GIS software, like ArcGIS Pro, has this tool built-in. Here’s how it works:

Pro Tips for a Smooth Mosaic

• Consistency is Key: Before you even think about combining your DEMs, make sure they all have the same coordinate system, cell size, and data type. I can’t stress this enough. Inconsistencies will cause headaches down the road.
• Fill the Gaps: Got gaps in your data? Consider filling them in before mosaicking. Interpolation techniques can work wonders here.
• Geodatabases are Your Friend: Seriously, embrace file geodatabases. They’re just better for storing raster data.
• Know Your Tools: “Mosaic to New Raster” is the go-to, but the regular “Mosaic” tool can be useful if you want to add DEMs to an existing raster.
• ArcGIS Pro is the Future: ArcMap is heading into retirement. Make the jump to ArcGIS Pro if you haven’t already.
• Pixel Type Pitfalls: Pay close attention to the pixel type! The default 8-bit setting can ruin your day if your data needs more precision.

Why Bother? The Payoff

Combining DEMs might seem like a hassle, but it’s worth it in the long run.

• Tidy Data: One DEM is way easier to manage than a dozen.
• Faster Analysis: Spatial analysis runs much faster on a single, contiguous DEM.
• Beautiful Maps: A combined DEM creates a seamless surface for visualization.

Final Thoughts

Combining DEMs into a single file geodatabase is a fundamental skill for anyone working with terrain data. By following these steps and keeping those pro tips in mind, you’ll be well on your way to creating beautiful, accurate, and efficient DEMs for all your mapping and analysis needs. It might seem a bit daunting at first, but trust me, once you get the hang of it, you’ll wonder how you ever lived without it.