Use shapefile to replace geometry in existing features.

[Adam Cox]

Hi all, I know this comes on the heels of the new information about the shapefile upload process, which looks great, but I thought I'd also throw this idea out there that I had a while ago:

Issue:  Highly accurate coordinates (or complex) geometries for resources are hard to get by digitizing from aerial photography through the web-map, because you are at the mercy of the accuracy and resolution of the imagery/basemap you are using.  However, the ability to create new resources through the web-map interface is one of arches' greatest strengths (in my opinion) because you use the correct forms/vocabulary and anyone can do it from anywhere.

Potential Solution:  To allow for an existing resource's geometry, whether line, point, or polygon, to be completely replaced with the geometry from a shapefile (or other spatial format).  That way, someone could add resources with passable, "placeholder" geometry and they would be fully functional resources in the database.  Later, the geometry could be replaced with better geometry, created in ArcMap/QGIS, received from a park or other entity, etc.  An example would be creating points for each building in a neighborhood and having people enter info/photos through the web-map.  Later, a shapefile of building footprints could be used to update the geometry.  Or, another example, create a point for a road, which would be a stand-in until a good centerline is obtained from elsewhere.

Anyway, it's a thought, and there may be related concepts in place that I'm unaware of.

[Dennis Wuthrich]

Hi Adam,

You've highlighted an interesting use case for Arches.  I agree that digitizing geometries from aerial images can only get you so far, and it would be great to use geometries from a GIS like ArcGIS or QGIS.

However, I'm not sure that importing a geometry from a shapefile for a single instance of a resource is the best approach.  We're currently looking at allowing users to drag and drop geometries into Arches via KML, gpx (e.g.: GPS files), and geojson.  This approach would still support multiple geometry types (point, linestring, polygon) that Arches allows you to define for a resource, which a shapefile (that can only support one geometry type) couldn't do.

I think that this approach does what you're hoping to achieve: allow an Arches data editor to easily add better, more accurate geometry representations on a resource by resource basis.

Cheers,

Dennis

[Adam Lodge]

Adam,

To further bolster Dennis’s point, you should know that ArcGIS, QGIS and most other desktop GIS software programs support the ability to convert data from shapefile to kml format.  There are also other free tools on the web that exist purely for that purpose.

Best,

Adam

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[Adam Cox]

Thanks for the replies.  Yup, it sounds like you are already putting these pieces together, and KML is a good format to use, because, like you said, there are lots of tools for conversions.

My thought was that a shapefile could hold many features, the geometry from each of which could be applied to a different Arches resource.  This could be done with a field that holds an ID for the Arches resource, or something similar, because shapefiles have easy tables to update.  Collecting good coordinates with a Trimble (or digitizing rows of buildings in ArcMap/QGIS) would then just be a matter of entering the Arches resource ID when you collect or create the data.  Basically, I'm considering ways to take advantage of the fact that coordinates (E47) seem to be relatively separated from the resource they represent (which is nice) as opposed to most GIS's where each data record is completely tied to its coordinates.  Also, it would help with "I just found a shapefile for all these existing arches resources, but I don't want to re-enter the info I've already put in the database".

It looks like there are lots of python modules for converting shp to KML or geoJSON (and reading dbf tables), so it may not be too hard to make a converter with those eventually.

Adam

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[Dennis Wuthrich]

Adam,

You've summarized a very interesting use case, and I agree that this workflow would be a convenient way to update geometries for many resources at once.  This kind of bulk "replace or append" edit is definitely something that we'll put on our radar.  If enough people think that its a desirable feature we'll put it on our roadmap for post 3.0 development.

-Dennis