[Talk-us] TopOSM Colorado

[Lars Ahlzen]

Bill Ricker wrote:
> What, MASSGIS doesn't cover Aspen?

Yup... too bad... :)

>> * Contour lines and hillshading generated from NED [1].
> 
> does that mean you're interpolating lines from a grid?

Yes.

>> * Hydrography (lakes, rivers, wetlands etc) from NHD [2].
> 
> which will eventually be in OSM

Yeah, and it looks like some good progress is being made. But until it's 
complete, I have to use the NHD data directly.

>> * The hillshading, contour lines and map features are on separate
>> layers. Use the layer switcher (top right "+") to toggle.
> 
> AWESOME. that's beautiful.

The main downside is that it increases the number of map tiles that have 
to be downloaded and makes scrolling choppy on slower hardware/browsers.

I think it's worth it, though.

>> Since the data is nationwide, the same technique could (theoretically)
>> be used to generate a complete TopOSM map of the US, or even the world
>> by using e.g. SRTM for elevation and OSM for hydrography.
> 
> requiring only a render farm plus some config ?

Yeah... well... for certain values of "some". It would actually require 
a fair amount of work. Here's my reply to another OSMapper asking me 
essentially the same question:

"That said, there are some obstacles to overcome before it can happen. 
For example:

A lot of manual labor is spent on downloading the data from USGS. Their 
java point-and-click interface (with lots of limitations on batch sizes 
etc) is not helpful for what I do, and nobody seem to mirror the data 
sets in a better format.

There's also the size of the data sets. The entire hi-res NHD and NED 
would probably be many, many TB. Unpacking, preparing and indexing that 
data requires plenty of additional disk space as well. One would 
probably have to re-work the scripts to work on smaller areas at a time, 
as well as invest in some sizable drives. The tiles themselves for CO 
are about 12 GB and 20 GB for MA, so I'd need a web host that's willing 
to host a TB or so of images. :)

Finally, Colorado alone took the better part of a week on my quad-core 
rendering server. And this excludes all importing and preprocessing of 
the data. Extrapolate for 48 more states..."

The above should not stop me from trying, though...


> Use any perl in ingesting or anything?

Wish I could say yes, but I'd be lying... it's all Python and Bash. :(

- Lars

-- 
Lars Ahlzen
lars at ahlzen.com