Getting Started With GeMS, Part A

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Getting Started With GeMS, Part A - An introduction to the GeMS schema, the GeMS Tools ArcGIS toolbox, and how to prepare ArcMap for digitizing.

The Geologic Map Schema (GeMS) defines a standard database schema — a database design — for digital publication of geologic maps. This tutorial is one of six originally presented as part of a short course at the 2021 Northeastern Section Meeting of the Geological Society of America by Ralph Haugerud, USGS, on how to use ArcMap and custom tools to create GeMS-compliant ArcGIS file geodatabases.

GeMS Trainings

  1. Getting Started With GeMS, Part A
  2. Digitizing an Analog Map With GeMS, Part B1
  3. Digitizing an Analog Map With GeMS, Part B2
  4. Digitizing an Analog Map With GeMS, Part B3
  5. Translating a Digital Map With GeMS, Part C1
  6. Translating a Digital Map With GeMS, Part C2


Date Taken:

Length: 00:07:56

Location Taken: US

Video Credits

Video and caption editing: Evan Thoms, Geologist, USGS,


Let's talk about getting started with GeMS.  These are the topics I will cover. GeMS is a schema for encoding the contents  of a geologic map in a GIS database. It is not a schema for encoding a geologic map image.  For that you might want Adobe Illustrator. Nor is it a schema for encoding the geology of the world. An opportunity to reimagine how we see the world. It's focused on archiving and publication of data for a single map in digital form. It may not be the optimal schema for field notes, nor publication-quality cartography, or for a multi-map database. It may be useful in providing clues towards such databases, though. And GeMS is, at the moment, unapologetically ArcGIS-centric. GeMS closely defines table structure in field names in a geologic map database.  It has only three embedded vocabularies. IsConcealed, an attribute of ContactsAndFaults, has values of 'no' and 'yes'. GeoMaterial, which is attached to MapUnitDescriptions, has about 100 values and  GeoMaterialConfidence, three values: high,  medium, low. All other terms, if used in a database such as bedding, contact, fission track date, fault, foliation or questionable, if they're  used in the database, are defined in the Glossary table and map units are defined in the DescriptionOfMapUnits. There are resources online for using GeMS and understanding it. The most important one, the one to remember, is the NGMDB GeMS page which has links to other resources listed here. The standard itself is a USGS publication, is rather dry reading,  but I recommend the introduction to you and some of the appendices. We're going to spend much of the afternoon talking about the GeMS toolbox, and GitHub.  I won't talk about that. You can build a GeMS database from scratch.  You can open up the documentation, see what the database schema looks like, make a new database, make a feature data set inside of it, look to see which feature classes belong inside that feature data set, what the fields are, how they're defined, and plug away. So you can do this from  scratch and you can manipulate the database with generic art tools. But this is the hard way. With  a closely defined schema shared tools become practical.  Over the last several years, Evan Thoms and I and a few others have built such a library of shared tools that make it much easier to work with the GeMS schema.  Let's fire up your favorite search engine and type into it UGSS GeMS Tools.  And we're looking for the GitHub site. Here's the landing page. I'm going to scroll down some here.  There's a readme that explains what we're looking at. This is a repository of Python scripts that run inside of ArcGIS for creating, manipulating, and validating GeMS databases. There are installation instructions.  Some advice on getting help. A plea for collaboration. And discussion of a few known issues. If we go back up to the top of the page. This here Is the wiki that I put together a couple of years ago for an earlier version of this short course offered at a DMT workshop in 2018. If you get excited about GeMS and like  to write and learn how to use it, would like to work on the wiki, that would be wonderful. Let's go back. We want to pick up the toolbox and generally, in general, you want the latest release. Click the link. Grab the zip file. And it takes a little while for GitHub to wake up and start shipping it to us. The file won't take long to download. Right now This of file is about 30 megabytes. And it's done. We can open the containing folder.  Grab the zip file. I like to keep my code in a code directory so it's separate from my data. I'm going to paste this here. If I look inside it contains a folder. I don't want a folder that's inside of a folder, so let's go back. And Extract All. And after a few seconds. The toolbox. A brief caution. This is the gem standard. The toolbox is not the gym standard, but Validate Database is intended to  follow the standard as closely as we can. In other cases, if there's conflict between the toolbox and the standard, the standard should be honored.  A brief note on directory structure, unless you're customizing the GeMS tool box,  it is easily replaced. It need not be backed up. Your ArcGIS data  and project files are near irreplaceable. They should be backed up frequently and for that reason keep your GeMS toolbox in one place and your data  and project files in another. Don't mix them up. Let's configure ArcMap. I find the default configuration doesn't work for me as well as it could, so I'd like to make a few changes. I've already opened ArcMap. Let's go in here.  We want to go to Customize, ArcMap Options and  make sure that 'Make relative paths the  default for new map documents' is checked.  I'd already done this, but in general when you open up ArcMap it's not checked.  The next thing you want to do is see you got your toolbars of choice and I like to work with this set. Advanced Editing. Editor. I don't like the Layout tool. Don't want it. I do want snapping.  I do want Standard and I want Tools and I want Topology available.  Extensions are not critical, but for my GIS work, I find it's very handy  to have 3D Analyst and Spatial Analyst  available without thinking about it. And then there's a sticky move tolerance and I want to go to the Editor. And Editing Options. And make sure this is set for some non-zero number.  Otherwise, when you select features, it's possible to move them inadvertently and the move, the move sticks and you've messed up your database.  You want to make it so you've got to make a definite move before  ArcMap recognizes that something  is going to be someplace else. So, about 20 pixels is a good answer. And then you want to install the Arc toolbox and Let's see. Let me open up the ArcToolbox window, right-click on an empty spot in there. Add Toolbox. Navigate to where you installed the toolbox. Go into the directory and if you're in Arc 10.5 or higher,  you grab this one. If you're an Arc 10 or 10.0 grab the other. Takes a few seconds. But it should pop up. There it is. And then you can right-click to  Save Settings to Default and maybe  the next time you open this MXD the toolbox will still be there.