Einstein, relativity, and ArcMap

The theory:

Einstein's theory of relativity has something to do with ArcMap... at least in the abstract. The theory states that measurements of various quantities are relative to the velocities of observers. And something about time being 'warped'.

Think of the world in this image as your map document and think of the warped grid as your network path --your 'Space'.

The problem:

Let's say your IT group installs a new disk in your network which is thankfully larger, making your work easier. They even moved your project data to this new drive. So let's say all your data and map documents are moved from the D:\Projects to the F:\Projects. Cool!

Well, not so cool, if you haven't prepared your work for this! In fact, this process may have been more like the "Big Bang"!

Every one of your layers now has than dang red exclamation mark, which we all know means the Source Property is broken.

Most of you already know the way to fix the red exclamation, but hey, why not make it so this doesn't happen in the first place? All you have to do is establish Einstein's Theory of Relativity before hand. (I know, I'm getting way too corny... but hey, I'm from Kansas!)

The fix: Relativity

Do this BEFORE the IT move. In ArcMap, open File > Map Document Properties...
Towards the bottom, check "Store relative pathnames to data sources".

That's it! Now when IT moves your Projects directory (which contains both your data and your map documents) from one drive to another, everything still works!

Using relative paths doesn't mean that the layers in your document will never need repairing. Even with relative paths, it is still possible for a document to be unable to find its data sources if the document or the data sources are moved to a different location relative to each other, such as to a different part of the folder hierarchy or to a different disk.

Read up in the help documentation for a few more details about relative pathnames as I didn't cover everything here. 

Recommendation:

BTW, you can set this as a default for every map document. In ArcMap, choose Customize > ArcMap Options. Check the Make relative paths the default for new map documents.

The confession:

I have no idea why I even connected this idea to Einstein's theory or the Big Bang... it just sounded like fun.

Happy GISing!

Reattaching a beheaded layer's heading!

A layer's heading -- NAME in this example.

You can behead it by clicking on the heading twice (no double-click). 

Then clicking the delete key. Click somewhere else in your table of contents and you get this:

What happens if you want it back? (I saw this posted on a list serve and thought this is a good tip to post on my blog.) It's quite easy, but sorta hidden.

Open the Symbology properties for the layer. 

Select (highlight) all the symbols you want to 'head'. Right click and choose  Move to Heading > New Heading...

Enter your new header name, NAME, shown below. 

Click OK. With the result, you now have your heading back. 

And it shows in your table of contents when you save the changes.

Remember, you can change the heading to anything you want either in the Properties or in the table of contents. 

You can also create a heading for groups of symbols. Give that a try! Have fun!