Digitize an Analog Map With GeMS, Part B1

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Digitize an Analog Map With GeMS, Part B1 - How to create an empty GeMS geodatabase in ArcMap, digitize contacts from a scanned geologic map, and create map unit polygons.

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: 00:21:58

Location Taken: US

Video Credits

Video and caption editing: Evan Thoms, USGS, Geologist, ethoms@usgs.gov


Let's dive into GeMS by digitizing an analog map.  We're going to work from a published paper map image, but it's essentially the same process as making new geology. When it's new geology instead of a map image, we have field notes that have been scanned, we have air photos, we have topography. But it's the same thing, you're looking  at an image and you are drawing lines on it. The processes are very similar. Will do this in steps with breaks for discussion between each step, We'll start by assessing the  source map, figuring out what we need. Making an empty database.  Putting a map outline, a box to draw inside of and begin digitizing contacts and making map unit polygons. Right now, I'm sitting at home in the west edge of Wenatchee in  the center of Washington State, and I thought I'd work on something local. So, we're going to look at the geologic map of the Chiwaukum 4 south  east quadrangle by John Whetten,  published in 1980s. A USGS Open file report. Here's a view of part of the map. It's a pretty ugly thing.  It was pretty clearly done as a blueprint type process and then later scanned. It's aged in the library.  The nice thing is that the National Geologic Map Database has a geotiff  and we don't need to georeference this image. To make life simple,  we're going to do the southeast one-ninth of the map so that there's a chance of getting through in the next few minutes. The first step is to inventory what's on the map. What kinds of features are present? What featured classes will be needing the database to capture them? We can see there are contacts, and interestingly,  none of them are dotted or concealed or are dashed approximate. They're all contacts, well-located. There map unit polygons.  And we've got several different units. Qal, Qoal, Qls, and then Tcs, which is an Eocene conglomeratic sandstone of the Chumstick Formation. And then there are these lines here, solid, dotted, dashed, solid with ornament along it and these are labeled. This is Tta. This over here is Tte. These are tuff beds.  And there's some question as to how they could be treated. Tuff beds like this, key beds, don't  participate in map unit topology,  thus they don't belong in ContactsAndFaults.  They could be stored in GeMS in either  GeologicLines or MapUnitLines and  the questions is which is appropriate.  And it's a matter of how they're defined. Geologic lines are identified by Type,  and they're defined in the Glossary table. On the paper map you look for the definition of that line in the explanation of symbols. Map unit lines are lines that are  map units and their meaning is defined in the DescriptionOf MapUnits table. In the paper map we see them in the DMU. On this map these shale layers show up on the  CMU, the correlation diagram, and they  are listed, not shale layers, tuff layers, they're listed as parts of the conglomeratic sandstone package. They're defined in the DMU, so they get stored in MapUnitLines in the GeMS database.  We also have strike and dip measurements, a fair number of them,  lot of them quite hard to read. To capture these we need four feature classes. We need ContactsAndFaults and MapUnitPolys and these are required in any GeMS geologic map database. We also need MapUnitLines and OrientationPoints which are as-needed feature classes. Put them in when you need them. Here's our recipe. We're going to make an empty database, we're going, by opening ArcMap, we're going to add reference layers to the map composition, including the scan of the map we're digitizing. We're going to save our MXD file as map name dash edit dot mxd. My experience is that editing and plotting typically need different reference layers and different symbolization. Thus, I use two MXD files for any map I'm working on, one for editing, one for plotting. We're going to run the Create New Database script. We're going to add a map outline to it. We're going to transfer the map outline into ContactsAndFaults. Fill out its attributes and get rid of the map outline. Then we're going to add a pre- packaged layer file that gives us digitizing templates. And begin digitizing the line work. We'll come back to this. So, here is the scan of the Chiwaukum 4 SE quadrangle. I've added some reference layers. For example, here are scanned USGS topo's off of the Esri Basemap collection and I happen to have LIDAR data for the area on my hard drive,  so I added that also. Part of the reason for doing this as I get really nervous about where things are located, georeferencing, mine and others. In more than one occasion I've found that. stuff isn't where I thought it was. And so let's go look at the corner of this map, right here. Turn the LIDAR off. The scan I made partially transparent. If we look at the base map, the scanned topo maps, we can see the seam in here. Where the scan, this quadrangle was joined to this quadrangle, this one to this one. There is a seam in through here. The quadrangle boundaries are in NAD27. This is the NAD83 tick and it's about 90 centimeters to the east-northeast of the corner. of the quad boundaries and it's this displacement between NAD83 and NAD27 that is a bugaboo. So let's put the scanned georeferenced map on top of here and, hurray, that corner is roughly where the corner is in the base layer. We can also go look at the LIDAR and I have a fair bit of faith that the LIDAR is where It's supposed to be. And we can turn this off and look, for example, at this little reentrant in here in the valley wall. And, yeah, again, it's about the right place, so I think the scan is properly georeferenced and we're OK proceeding. The next step is to make an empty geodatabase and so we want to open up the ArcMap toolbox. Create New Database. Go to the output workspace and it's Chiwaukum 4 SE. We're going to call this And, ordinarily I would say copy the reference framework from the input base map. But NAD27 is a bad actor for many people, so let's not do that. I'm going to copy it from the LIDAR data in here. and one of the LIDAR datasets is in NAD83. UTM 10. Let's use that. We need feature classes and elements that are beyond the standard required GeMS minimum. We figured out that we needed to have GeologicLines. Sorry, MapUnitLines. And OrientationPoints. We don't want a cross section. We're not going to enable data tracking. We're not going to use cartographic representations. We do want to add LTYPE and PTTYPE and we'll see why shortly. And in general we want the standard confidence values, certain and questionable added to database also. Click OK and it runs. Won't take very long. We can sit here and watch it. It'll tell you what it's doing to keep you entertained, but also while coding, this was nice to know what was working or wasn't. And if you get an error in this Evan and I, who have done most of the coding, we would very much like to hear about it. And the best thing you can do is give us. A screen grab of this output, so we can see where the error occurred. One minute, 8 seconds later, it's done. And we can close this window. And close the toolbox for the moment and we can add data to our map. Here's our database. And we want to add the ContactsAndFaults. And MapUnitLines feature classes to the map composition. They are empty, nothing shows. The next step is to make a map outline of a box to draw inside it, and there's a tool here that makes that easy. The challenges that map outlines are roughly rectangles, but in detail they are not. They need lots of points to control them. We want to know, move some windows here, we want to know where the box is going to be. And for that we look at our map. Very conveniently. it's got nice even coordinates. The southeast longitude is west -120 30 minutes. .5. SE latitude is 47.5. 7 1/2 minutes is the full quadrangle width. We're going to do 2 1/2 minutes to get a ninth of the quad, but if we put this in here, it will think that, values less than five are assumed to be in degrees, so we'll get a 2 1/2 degree box, so we need to value that is in decimal degrees, and for that it's time for the calculator and 2.5 / 60 equals 0.04167. And, we don't care about tick spacing The output is indeed NAD27. The output geodatabase. We can write this to the database where building things in. The output coordinate system we want to use NAD83 UTM 10. And the Scratch Workspace, we have an empty folder here. We're going to use that. And this should run, it's done. You should be able to open the catalog. And, uh, there is our map outline. You can add our map outline to the composition. And there is, it's a thin red line. Let's make it a little thicker. We do not need our reference layer. That just slows us down. So the next step is to transfer this map outline to ContactsAndFaults and there are several ways to do it. We can copy and paste, we can load. Copy and paste works pretty well, so we want to make this. Editable. And select it. Copy. Paste. We'll want to paste it into ContactsAndFaults. We can turn this off and there it is in ContactsAndFaults. Let's give us some attributes. So the Type is 'neat line'. It's not concealed. We calculated its location, so we know exactly where it is. We're certain. That it exists. Um, we're certain what it is. And at the moment we don't care what the label of the symbol is, and let's see the DataSourceID blank also for the time being. Now we've got a box. We got something to do digitize we're looking at. Let's make this easy. We're going to add a layer of templates that allow us to digitize features without having to figure out too closely what all their attributes are and we're going to go to Add Data. And go back to the GeMS toolbox which is living here. And into the Resources layer and find ContactsAndFaults24K and add it. Um, ContactsAndFaults24k references a ContactsAndFaults layer, but it doesn't know which one, so there's a problem here. We need to click on one of the layers. Data. Repair data source. And go back to our new database. And select the ContactsAndFaults layer. Everything now knows where its from. These layers, each one is visualizing a different attribute of ContactsAndFaults. This one's telling us what the LTYPE is. This one's being symbolized on the base of existence confidence. This one identity confidence. And so on. And the nice thing about this layer also, let's move in and zoom a little bit in here. If we decide to start digitizing. Let's see, we're editable, OK. We want Create Features window. We want to remove ContactsAndFaults from here. We want to remove MapUnit. Lines. Stop editing. Yes. Ah, there are our templates. So, if we look at one of these here. It's got a name. It's a line. It makes a new feature if we use it that's got a type of contact. It's not concealed. It's got a certain existence and identity confidence values. Has Location ConfidenceMeters value of 100. And it's, um, references an LType of 'contact 100m'. That's why we see it here on this menu. So I can take this. Now, let's back up. This is a 24,000 scale map. These are all certainly- located contacts. Interestingly, we put the base map in, you may be able to see here that the contact on the scan does not line up exactly with the contact and then the line uh, scanned 24K. I think what this is showing is a measure of the distortion involved in making a map, Printing it on paper, storing in the library, and then scanning it again. So, features have been shifted by the history of this map, and I'm reluctant to say that we know where things are within 1 millimeter maps scale in this, so I'm going to digitize these all is having a 30 meter LocationConferenceMeters. Let's start by digitizing this contract right here. We can start, click. And here we get our contact. We do the next line. And as you may notice, snapping is enabled. This is the ArcMap configuration we set up in the First bit here earlier. I know this is really exciting to watch. I won't bore you too much more. I can turn on the LCM layer and here gray, gray halos showing us on the map what a 30 meter Location ConferenceMeters value looks like. It may be that I'm being too conservative and we can call these 20 meter LCMS, they're almost certainly not 10. If we don't like this. We could open the attribute table. Then change these values. That 10. And the halos are skinnier. I do not think those lines of that well located. Let's stick with 30, so let's see, Edit, undo database row change and edit,  undo database row change, and we're back at 30. We have the map boundary. And this contact that makes a closed polygon and this contact that makes a closed polygon. We can make polygons now. Before we do that, I'd like to see what we have selected here, so let's, uh. Zoom to selected features. If we build polygons from this, well, let's do it. Make polys. Oh, we need to have polygon features in here, a polygon layer to make polys into it. So let's add MapUnitPolys. Now we can build polys. And this will build polys in MapUnitPolys. And we do not want that polygon. That was sort of the local universe. We can keep deleting those when we ever we build polygons or we can chop the map boundary up in little pieces so when we grab it, we don't grab all of it. Oh, here we want. OK, that'll work. Let's do one more line here. Piece of line again, we're going to call it a 30 meter contact. We can select the map boundary. Select contact. Build polys. OK, that polygon, look at its attributes. That is, like everything else in here map unit Tcs. It's like this one. It's like this one. Let's do. One other map unit here. Other polygon. And again, want my template. 30 meters. Now it's not going to snap because we have not enabled Snap To Sketch. If we enable that, we can connect to the line we just true. We didn't, so disconnect this now and it will snap. There's a closed polygon. Select that. Construct polygons. That one. Qoal. We can now double-click on this. Go to the symbology field, symbolize it by unique values of map unit. And let's pick some colors that make sense to us. That's a nice Eocene. so I'm going to call it green. Show color orange. Eventually we'll color the map based on the symbol field, but while we're building the map that's inconvenient, it's not easy to transfer symbol values from the DMU to here so in the early stages of building a map, I typically symbolize directly on map unit and change it later. I'm going to stop recording this and go digitize the rest of the map and will come back later.