DIFFERENCE BETWEEN COVEREGE / SHAPE FILE
gbar75
Are there any sites that explain it ?
Thanks in advace.
Giorgio
Michael Colavito
My understanding of a shape file is that it is ESRI's propertiery format
for storing graphic data only. A coverage is all the data, graphic and
attribute that make up a particular theme i.e. land use or soil types.
A coverage has topology. Hope this helps,
Mike Colavito
bra...@attglobal.net
Shapefiles are not proprietary, the format is published in a
white paper available from ESRI's site. Also, shapefiles store both
the graphics and attributes of spatial data, not just graphics.
The minimum number of files needed to make a shapefile
is 3 - a .dbf with all the attributes (one record for each graphic
element), a .shp file that contains the coordinate listings for each
graphic attribute, and an .shx, which is some kind of spatial
index, I'm not sure how it works internally. There are a few
more optional files, such as .sbn and .sbx, but are not required.
The coverage is a proprietary format from ESRI, which is geo-
relational and has full arc-node-polygon topology, provided the
GIS users issue the correct methods of data maintenance (clean,
build, fuzzy tolerance, dangles, etc.). From the operating system
perspective, a coverage is a folder or directory
containing various individual files. Also, there is a single "info"
folder or directory for each folder/directory containing coverages.
Although there can be multiple coverages in this one folder
or directory, all the attribute information is stored in the single
info folder/dir, assuming the user is using traditional coverage and
not something like SDE, which is a whole other ball game.
Basically, shapefile is easier to use and understand and requires
less maintenance but does not support detailed spatial analysis that
a format with full topology supports.
--
"Michael Colavito" <mc...@worldnet.att.net> wrote in message
news:3A21506E...@worldnet.att.net...
bra...@attglobal.net
I made a typo that I thought was worth another post for
correction. The .shp file contains the coordinate listings
for each graphic ELEMENT. I said "attribute" the first
time. Sorry for the brain fart.
--
<bra...@attglobal.net> wrote in message news:3a218...@news1.prserv.net...
Michael Colavito
theme has attribute information, how would this differ from a "coverage"?
Isn't it the same thing or very similar? Is the difference, the ability or
inability to do GIS spatial analysis on the theme?
Thanks,
Mike
bra...@attglobal.net
It's not as black and white as the ability/inability to do spatial analysis.
Some spatial analysis can be done with shapefiles, but analysis is
not a strong point of shapefiles. The coverage data model has
more intelligence inherent in it's internal structure. For example, each
polygon
in a polygon coverage is aware of each arc that makes up its boundary,
and all the other neighboring polygons, just for example. A polygon feature
in a
shapefile does not know this information. With shapefiles, you can digitize
polygons on top of polygons and not worry about maintaining topology,
yet this is much more difficult in the coverage data model.
The advantages and disadvantages between data models are
becoming a non-issue with more powerful software being released.
The shapefile format sucks in many instances, and yet so does the
coverage. The large majority of GIS activity is in the spatial "inventory"
arena, as opposed to spatial "analysis" so the choice in data model is
really
dependent on the user and his/her/their needs and environment (hardware,
software, databases, etc.)
--
"Michael Colavito" <mc...@worldnet.att.net> wrote in message
news:3A21B748...@worldnet.att.net...
Ron Natalie
bra...@attglobal.net wrote:
>
> Shapefiles are not proprietary, the format is published in a
> white paper available from ESRI's site. Also, shapefiles store both
> the graphics and attributes of spatial data, not just graphics.
> The minimum number of files needed to make a shapefile
> is 3 - a .dbf with all the attributes (one record for each graphic
> element), a .shp file that contains the coordinate listings for each
> graphic attribute, and an .shx, which is some kind of spatial
> index,
The shx isn't a spatial index, it's just a file with elements that
are fixed length that gives you the ability to rapidly index into
the variable length entries in the SHP files.