Assuming you've done all the googling you can stand, looking for "world
city shapefile" and strings like that...
In my experience of dealing with data, and recognizing the tools that
are available for cleaning things up, if I were you I would start by
converting the datasets you find interesting into a common format that
you can edit, say shapefiles.
For this conversion process you might use ogr2ogr or you can try
camp2camp. By the way, though I say this without any personal
experience, I would imagine that compiling ogr2ogr for the Mac should
not be horribly difficult.
As you begin to collect your data in shapefiles, you can use OpenJUMP to
edit it, for instance by selecting the data of interest, copying and
pasting it into a new layer, adjusting the tabular schema, and saving as
a new shapefile. There are other alternatives to OpenJUMP, such as
QuantumGIS, but I've had some good experiences lately cleaning up data
with OpenJUMP. If a substantial number of datafiles exist with the same
schema, and the schema is suitable to you, you can perhaps just pull out
the information of interest with the ogr2ogr selection capability and
avoid all the pointing - and - clicking.
When you're done with the edit / cleanup step, you should have a great
number of reduced / edited / restructured datasets that fall into groups
with similar attributes, that you've made as similar as possible through
your editing / cleanup.
At this point you can use ogr2ogr or camp2camp or shp2pgsql to import
your datasets into PostGIS.
Your last job would be to write some SQL that would massage your data
into a final coherent structure.
This is not a trivial project! Unless you get very lucking in your
search for starting datasets.
If I were contemplating this project, I would be wondering about things
like "how valid are these city polygons I'm finding, anyway - do they
represent the actual 'city limits', where such things exist? or were
they some visual boundary compiled by the map maker? or something else
entirely?" Think about big, free-styling cities like Mexico City or
Lagos in this context. And remember that urbanization doesn't usually
halt at the 'city limits'.
Anyway, good luck. You can write to me off-list if it seems that your
queries are getting too distant from the subject matter of this list.
anders conbere wrote:
I'm trying to do some work with cities, but struggling to figure out
first how to get polygon data about the worlds cities and second how
to patch together many different formats and files into a singular
postGIS database
Say for instance all the Tiger/Line data...
I would be more than happy to build a US set of data based on that for
city polygons, but they're not in shapefile format (and ogr2ogr isn't
available on my mac, though I can convert them on my linux box at
home), and I'm not sure I understand who the shapefile importer works
in terms of clobbering data already there etc.
anyway... I guess I'm lost and looking for ways to deal with all the
vast different paths doing google searches for GIS seams to take you.
~ Anders
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Regards,
Chris Hermansen · mailto:[EMAIL PROTECTED]
tel:+1.604.714.2878 · fax:+1.604.733.0631
Timberline Natural Resource Group · http://www.timberline.ca
401 · 958 West 8th Avenue · Vancouver BC · Canada · V5Z 1E5
C'est ma façon de parler.
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