FAQ: Map Options and Features

Q: Where did the Blue Marble maps come from?

A: The Blue Marble images were created by NASA using data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS), an instrument aboard the Terra satellite. Please see the Great Circle Mapper credits for more information.

Q: What is the difference between Blue Marble and Blue Marble: Next Generation?

A: NASA released the original Blue Marble imagery in 2002, using data from the MODIS instrument (see previous question). Two years later, NASA released Blue Marble: Next Generation, again using data from MODIS but with improved image processing techniques and observations spanning an entire year. The newer imagery also featured higher resolution, with a single pixel representing a square 15 arc-seconds on a side versus 1 arc-minute (60 arc-seconds) for the orignal Blue Marble imagery.

The Great Circle Mapper's Blue Marble maps use the Next Generation imagery.

Q: How can I make different paths use different colors?

A: Consider the path SFO-DFW,SFO-IAH with the default path color (red). Changing the color for just SFO-IAH to navy blue can be done using the path SFO-DFW,color:navy,SFO-IAH. You can shorten color: to just c: and can changes colors as many times as you like.

Valid colors include those offered for any of the color options in the Map Controls. In addition, colors can be specified using hexadecimal colors using a syntax like that used by CSS. For example, c:#ff0000 is the same as c:red.

Q: How many points/paths can be on a map?

A: The Great Circle Mapper software has no architectural limit and is only limited by memory on the server (and patience). On the development server a map with 84,532 paths was generated with no problem.

The length of a URL does limit the complexity of maps which can be requested, however. Internet Explorer has a maximum URL length of 2,083 characters which is probably the most restrictive limit. Most other browers are less restrictive, in which case the limit becomes the length of a request line accepted by the Apache HTTP Server software. This limit is less than 8,190 bytes.

Work is underway to allow map definitions to be saved on the Great Circle Mapper web site which will allow more complex maps without exceeding HTTP's limits on URL lengths. (There is not yet a target date for when this work will be completed.)

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