3. CREATING DATA (First steps)
3a. Geodatabases and Feature Classes
3a. Creating data
Now that your field map is georeferenced, you are ready to digitize it and create all sorts of geologic geospatial data. None of the steps in this process are too complex or difficult, but do need to be done in a certain order for your data to be created properly. Please pay attention to the order in which things are done.
Creating a geodatabase
All the data you create for your geologic map (point, line, and polygon shapefiles) will be stored in a geodatabase. To make a geodatabase, open up ArcCatalog and navigate to your workspace (refer to the ArcCatalog figure at the beginning of this tutorial for where these things are). Right-click in the big window on the right and select New –> Personal Geodatabase. Name it something appropriate, being sure to follow your good friend the Rule of Names.
Now you have somewhere to store all the data you’re about to create.
Creating a feature dataset
A feature dataset is a container to hold related map data. This is sort of like a “sub-database” within the larger geodatabase. Feature datasets hold related geographic information, such as all of the features that comprise a single geologic map. These are necessary so that you can relate and convert information, such as taking a set of lines and creating polygons from them. Here are the steps to create a feature dataset:
1. Open up the contents window of your personal geodatabase. Simply done by double-clicking on your geodatabase icon in ArcCatalog.
2. Right-click in the “Contents Window” and select New –> Feature Dataset.
3. Give it an appropriate name. Since this dataset will contain primarily geologic information, go ahead and name it something like “geology”.
4. Next you’ll be asked to define the projection/ coordinate system for the dataset. Use the same system that you did earlier when setting up your ArcMap project. In the example for this tutorial, we’re going to select Predefined –> Projected Coordinate Systems –> UTM –> NAD 1983 –> NAD 1983 UTM Zone 11N. Once you’ve selected the projection, click “Next”.
5. Don’t worry about choosing a vertical coordinate system at this time. Click “Next” in this window.
6. This next window asks about your preferences for precision. The defaults are plenty good for this one, so go ahead and click “Finish”.
Your feature dataset will now appear as part of your geodatabase. But the dataset is still empty!
Now we’ll actually create the files that will contain your map data. Here, we’ll walk through creating line and point feature classes, and assigning topological rules to the lines so we can construct polygons from them- all done within ArcCatalog. First up is creating a line class.