The first question you need to ask when writing a University course, setting up a company or becoming a politician is 'who am I helping?'. Its no different with a Google Earth project, you have to consider the range of people who will use your resource.
My former employers, the Open University in the UK, used to have a good exercise for focusing on this problem; they used to try and imagine the spectrum of people taking one of their online courses and identify what people were like at the ends of the spectrum. The course needed to be a compromise between these users and their different needs. Thus we had discussions about whizzy Wilma, a power IT user who would be frustrated by the lack of features in a course and would want things to download quickly. Her most valued belonging was her Blackberry. Or tentative Tony who was retired and wanted the web pages to be very straight forward as he was not comfortable using the web. He usually wore slippers. Know-it-all Noel was a particular favourite of mine, a medium level IT user his problem was that he had already knew the topic being taught much better than everyone else and was always trying to prove this in his emails to other students and his tutor. We imagined him to have terrible taste in golfing sweaters...
(photo courtesy of headur from www.flickr.com)
These users are not only found taking Open University courses, they also use Google Earth projects. A lot of projects seem to be aimed at know-it-all Noel, there are lots of layers showing an amazing array of photos, text and other information but not much thought put in to helping tentative Tony. He needs some kind of introduction and some gentle but brief guidance on what to start looking at.
An introduction should cover the main topics (no more than 3 I think) that the project helps with. This could be a series of bullet points or questions. Then a brief section of text covering the data, when I say brief I mean 50 - 100 words, any more and the user will skip it, no one but no one reads instructions properly these days. I don't think its a good idea to guide users in how to use Google Earth in an introduction, you have to rely on them knowing that for themselves and you only have 100 words but they need to know about what they can find in your project.
I think there are three main ways of delivering an introduction to a Google Earth project;
1 - an introductory folder at the top of the project which has a pop up bubble with the text in it. I usually name mine 'Read Me First!' so that users are in no doubt what it is.
2 - An overlay image that users cannot avoid seeing and therefore reading. The image is a screenshot from the Explore Artic Drilling project I was talking about last week. I'd like to be talking about another Google Earth project but this one was the only one I could find quickly with a good introduction
3 - A video fly through of some of the main features of a project. The Digital Urban folk and I kind of came up with this when I spoke to them recently. I'll explain how later but to show you what is technically possible with a video this is one of theirs taken of Google Earth;
Helping users is the important part of this post when compared to introductions, our trio of imaginary users are a group we will be considering again I'm sure. I'll leave you with a link to creating passionate users, a sadly defunct blog about user support. Well worth a read.