How do I create a new feature class/shapefile?
This post covers an essential skill – creating new feature classes and shapefiles. We’ll cover how to create a blank layer and then how to digistise new features into that.
Creating you own data layers is an important part of most analysis projects, so in this post I’ll cover some of the essential steps in creating new feature classes or shapefiles. Maybe you want to add some points so you can do some viewshed analysis, or you need to create a layer that you can use to clip out some data. The process is pretty much the same for both so initially I’ll focus on feature classes and finish up with what’s different with shapefiles. In the following example, I’ve got an aerial photograph of Quail Island in Lyttelton Harbour and I want to create a new layer of walking tracks from what I can see on the image. Here’s the image:
If you look closely you can see the tracks – later on I’ll be able to use this to create the new features. Let’s assume I’ve got an existing geodatabase in a folder on my H: drive and I want to add the walking tracks layer into that. In ArcCatalog, navigate to that folder and right-click on the geodatabase; choose New > Feature Class. (You can also do this from the Catalog window inside ArcMap.) We’ll step through a few windows to create a blank feature class and then digitise in some new features. To create the new feature class I’ve got to set a few parameters. In the first window you can set the layer name, an alias (this is what will get displayed when the layer is added to a map) and a feature type. The most important part of this step is ensuring that you’ve set the feature type to line in this case:
Click Next and then we can set the coordinate system. For the most part, there are two main coordinate systems that interest us: New Zealand Map Grid (NZMG) and New Zealand Transverse Mercator (NZTM). NZTM superseded NZMG and the vast majority of the data on J: are in TM so I will set it to that coordinate system. The path is Projected Coordinate Systems > National Grids > New Zealand > NZGD 2000 New Zealand Transverse Mercator.
(Note that you can add this to a Favorites folder to make it easier to find next time.) Accept the defaults in the next two windows and click Finish to create a new blank layer. You can now add this to a map so that the walking tracks can be digitised.
Creating a new shapefile is a slightly simpler process as once you’ve right clicked on the data folder (not the geodatabase) and selected New > Shapefile, there’s only one window needed to specify the parameters. Both types of blank layer can then be edited as outlined below.
Creating new features – digitising
The process of creating the new features is called digitising. To get started with this we need to open an editing session – this can be done by first adding the Editor toolbar; right-click on a blank area of the menu at the top and select the Editor toolbar (Alternatively, click the Editor Toolbar button next to the scale window: (). Click the Editor menu and go to Start Editing. All going well, most of the buttons should now be active:
We want the Create Features button at the far right. Clicking this adds a new window to the map.
If there’s not entry for the layer when you open this window you just need to create a new template. Click the Organize Template button, , and then click the New Template button, tick the box next the layer and then Finish. In the Construction Tools window I can select a particular tool to suit my features – here I’ve got the default line selected. Once you’ve selected a tool, the cursor switches to a set of cross-hairs and you’re ready to digitise. Back on the map, click once to start the feature, once for every vertex (direction change) and double-click on a feature to finish it off.
If I open up the attribute table, there’s now one record in there which is the feature I’ve just digitised (and since this is a feature class in a geodatabase we’ve automatically got a length field for that feature.)
At this point I’d like to add in an attribute to allow me to label each track with a name. An important thing to note is that I can’t add a field to the table if I’m in an editing session so I need to first go back and turn off the editing session (and save my edits.) Click on the Table menu at the far left of the table menu buttons, , and go to Add Field. I’ll add this as a text field with the default width and call it TrackName.
Now go back and start a new editing session. With the table open I can click on a cell and add text.
Now I can go back to the map and add more track segments or edit the feature I’ve already digitised. Since I’ve got some text for labelling I can display that also:
Creating points and polygons is quite similar, though some of the options with polygons get a bit complicated; something I’ll have to cover in another post.
In this post we’ve seen how to create a new, blank layer (either a feature class or a shapefile) and then how to digitise in new features (and attributes as well.) The raster model is a very different story when it comes to creating new layers; another post as well.