[postgis-users] new to gis, trying to get started

[anders conbere]

On 10/27/07, Chris Hermansen <chris.hermansen at timberline.ca> wrote:
> Assuming you've done all the googling you can stand, looking for "world
> city shapefile" and strings like that...

*groans* yes... what a worthless set of results

>
> 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'.

Luckily I'm not in great need of accuracy so much as the "general
idea" of the city.

>
> 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.

Thanks so much! it feels great just to hear the words of someone who
might have an idea of how all these pieces go together. It's been
quite the daunting week of reading and learning.

~ Anders

>
> 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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> > postgis-users at postgis.refractions.net
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> >
>
>
> --
> Regards,
>
> Chris Hermansen · mailto:clh at timberline.ca
> 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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