[Live-demo] Natural Earth in 4.5b2

[Brian Hamlin]

Hamish-

   I am just finishing a set of tables cleaned via st_MakeValid() in 
PostGIS 2.0b
Conveniently, I renamed the tables as c10m_this_that
  so as to no longer need the quoting..

I wonder how many people use the .shp files..
or how we should name those..

   -Brian


On Feb 24, 2011, at 8:21 PM, Hamish wrote:

> Nathaniel wrote:
>> I'm not seeing the any geometry errors in ArcGIS (the horror,
>> the horror) on the 10m lakes theme fresh off the website.
>
> Arc is not a topological GIS so it misses (or ignores) many
> errors in the data which cause problems when the data is used
> in other ways which demand topological correctness.
> ([river] network analysis, etc)
> I understand that Natural Earth is mainly focused on cartographic
> needs, but ...
>
>
>> The 1.3 version that was released a couple weeks ago should have
>> resolved most the obvious topology errors on the themes that
>> were ID'd to me before. If you want to run a custom repair
>> geometry / topology script on them as they're imported to the
>> LiveDemo system, sounds fine to me.
>
> Loading a fresh download of 10m-lakes.zip into GRASS GIS (which
> is fully topological) exposes a number of errors in the data.
> Probably most are due to overlapping areas; small sliver areas
> resulting from those after "flattening" are appear below as
> areas without centroids (no attributes).
>
> GRASS65> v.in.ogr dsn=natearth/10m_lakes.shp out=ne_10m_lakes
> [...]
> Building topology for vector map <ne_10m_lakes_tmp>...
> Building areas...
>  100%
> 1708 areas built
> 1472 isles built
> Attaching islands...
>  100%
> Number of nodes: 2627
> Number of primitives: 4691
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 4691
> Number of centroids: 0
> Number of areas: 1708
> Number of isles: 1472
> Number of areas without centroid: 1708
> -----------------------------------------------------
> Find centroids for layer: 10m_lakes
> -----------------------------------------------------
> Write centroids:
>  100%
> WARNING: 82 areas represent more (overlapping) features, because 
> polygons
>          overlap in input layer(s). Such areas are linked to more than 
> 1
>          row in attribute table. The number of features for those 
> areas is
>          stored as category in layer 2
> -----------------------------------------------------
> 1358 input polygons
> Total area: 1.26155E+12 (1708 areas)
> Overlapping area: 2.02361E+11 (82 areas)
> Area without category: 2.39549E+10 (240 areas)
> -----------------------------------------------------
> Building topology for vector map <ne_10m_lakes>...
> Registering primitives...
> 3489 primitives registered
> 138259 vertices registered
> Building areas...
>  100%
> 1708 areas built
> 1472 isles built
> Attaching islands...
>  100%
> Attaching centroids...
>  100%
> Number of nodes: 3253
> Number of primitives: 3489
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 2021
> Number of centroids: 1468
> Number of areas: 1708
> Number of isles: 1472
> Number of centroids outside area: 3
> Number of duplicate centroids: 5
> Number of areas without centroid: 248
>
> #extract problems to another layer:
> GRASS65> v.extract in=ne_10m_lakes out=ne_10m_lakes_problems layer=2
>
> displaying that extract shows problems are all in the northern
> hemisphere, the Great Lakes of N.America being the biggest
> pile of red ink. (Lakes Ontario and Erie look ok though)
>
> a map layer created with "v.clean error=problem_areas_map" can
> help quickly pinpoint where the problems are.
>
> e.g. an easy place to start looking are the finger lakes within
> this bounding box, all of which show errors:
>
> north:      43N
> south:      42:18N
> west:       77:24W
> east:       76:12W
>
> (south of Rochester-Syracuse, NY)
>
>
> best,
> Hamish
>
>
>
>
>