Re: Sharing downloaded maps
- View Source--- In USAphotomaps@yahoogroups.com, gnuarm.2006@... wrote:
>That was the initial reason for the proposal
> That way you can easily grab a specific area without having to manage the download.
>I've thought of that, too. But writing and shipping DVDs of these really big datasets (Seattle Urban is over 12GB, I have no idea how big San Fransisco is going to be) would be pretty expensive both in time and money. Still, it might be somewhat preferable to terrafetcher.
> While I think this data would be better shared by shipping DVDs,
> bittorrent would provide a more available access.
> But to make it work will require that the entire country be broken > into pieces that will be easy to manage.The Urban areas are already conveniently broken up, since they are all islands of map data. The beauty of bittorrent is that it is ideal for really huge downloads. I've downloaded multi-GB torrents of entire TV series. The point about breaking big areas in to smaller groups of rows is well taken. Typically many files can be combined in one torrent and the downloader controls the priority of each file, so he or she can use rows as they are completed and doesn't have to wait for the entire torrent. And not just photos and topos. Tiger Streets, Elevation Data, and any other stuff the program may become capable of downloading are candidates for this type of file sharing.
There's no need to zip groups of files unless there is a substantial size advantage. Torrents handle multiple files just fine.
The limiting factor is the size of the swarms that can be built up. A swarm is bittorrent terminology for the group of participants involved with a torrent at any one time. The efficiency of of the system depends on a substantial number of people downloading the same torrent simultaneously. Typically, torrent downloaders run their computers 24 hours a day. Smaller workgroups that use bittorrent to share work product either have to agree to do the same, or coordinate time periods when most or all of them are connected.