For this icon graph design assignment, I was asked to do a series of icons for travel industry to represent trains, spaceships, and time travel.   Allow me to ask you a question first: what do you enjoy most about a trip?  Is it the final destination or the view alone the way? Is it the excitement of seeing the place you’ve been dreaming for a long time or is it the unpredictable discoveries? Technologies are rapidly changing our travel experience, nevertheless no matter how fast it evolves, no matter which transportation you choose to ride, a map seems always handy and essential. Eventually, a semi-folded map and location pin became my key visual elements of this icon set.

Initially I did think about the train as train itself and spaceship as spaceship itself. However, we are missing the time travel transportation here. It is not available to us yet. And it will be inconsistent for the whole icon set.

Thus I think about the dimensions.
2D Travel
First of all, train is constrained by the tracks. It is an A to B linear transportation. I summarized train travel as a 2D transportation: dotted white line as the track, location pin as destination, with a map on the background, the train travel icon is developed.
3D Travel
In terms of spaceship, it is a bitter fancier, it can travels from A to B to C as a none-linear track. I summarized such travel as a 3D transportation. Space itself is, as far as we know, infinite. And I believe every boy once had a dream to travel to the infinite universe yelling Buzz lightyear’s quote “to infinity and beyond!” Childhood memory is still fresh at this very moment. Thus a white infinite loop symbol was developed for spaceship travel.
4D Travel
For the time travel, obviously it is 4 dimensions transportation. Time becomes a tangible track. In order to illustrate this extra dimension, I put the minute hand beyond the semi-folded map, let it goes beyond 3D space into the 4th dimension.