Experimenting with travel time maps (see also my other page) in a city, I clearly observed diamond shapes, typical of what is called the Manhattan distance (travel time in a place with perpendicular streets). It is also called a taxicab geometry and the diamonds are actually “circles” given this distance.
Let's switch to more useful stuff. If you are travelling to New York, you might be interested in travel time maps by foot and public transport, for example to find a hotel. As shown below it gets more complicated as the metro creates shortcuts, thus you can see the diamonds but there are multiple centers. Here are travel time maps at different scales travelling from/to Times Square (click for bigger image).
Let me know if you are interested by getting/buying less-compressed/larger maps or from a different place. (contact: click-me ;-p @nospam.com)
Any feedback or remarks? Contact me at click-me ;-p @nospam.com.