Identifying Raster Cell values in ArcGIS Online

07-18-2016 11:04 AM
Status: Open
Frequent Contributor

Identifying Raster Cell values in ArcGIS

This is a common use case - we want to Identify on a DEM raster (imagery) in a webmap and get a popup showing the elevation (the pixel value).  I figured out how to do this as in the first link above. But, we need it in the webmap. We like the ArcGIS  because its popups "just work".  

Here is an example:  Identify cell value with Popup in a mapServer raster  It works for a map image layer i.e. ending in /mapServer.

I had already coded an identify to show only visible layers in the popup in a custom API 3.7 viewer, based on threads with Ken Buja et al back in the day, but we are now solidly onboard the Web App Builder train. The workflow we have created now puts all layers in to one service and the DEM imagery is one of the sublayers. 

The way we use the webmap popup, is I turn it on for every single layer. That way, if a user clicks on the map, info comes up, for any visible layer. No 'Identify' concept etc. I have found users absolutely love this.    It's discoverable and immediately intuitive. I wish the back/forward < > buttons were a little more prominently displayed perhaps, but, I have found after training a few hundred staff that I explain it in a few seconds showing paging between a few different layers that I identify on, and they get it immediately and like it.  So, Identify on a raster would be very useful. For elevation, and perhaps categorical rasters like land cover.


Related idea:


Yes I presume they'd also like point and click Identify for values like DEM elevation.

Surprised this is not getting more traction. Most people in the world live on the coast! Ground elevation is an important part of a web viewer for any local or regional government web viewer...  I could build an Identify but ... time. And keeping it working with API/WAB.  The best part though about webmap popups is not requiring users to "turn on an Identify" or worry about "tools".  I have noticed users LOVE this because  it is discoverable. And no learning how to use a tool.


It'd be useful to have the elevation displayed as a label on the map.


You could publish the DEM as a Elevation service and then use the elevation widget in WebAppBuilder Against it. Or you could Raster to Polygon—Conversion toolbox | ArcGIS Desktop  and then publish as Feature Service and lablel that.


Philip, those are both good ideas and at some point, I will probably set up an elevation service to use our lidar DEM and DSM. However, there are other kinds of rasters like land cover this would be very useful for and also this method is much simpler. Also, often you might for example get a raster either mapserver or imageserver link from another agency, that doesn't provide an elevation service. Since it's "technically" possible and one line of code to implement, I'd think this would be a priority for the AGOL in a future update.

Our services changed. I updated my raster value popup example, below.  I still believe it would be very useful for Esri to implement this official in the API, WAB, and ArcGIS  / webmaps.

Raster popup Example:

 Identify cell value with Popup in a mapServer raster  


Another use case I'd like to see this applied to is World Imagery to get the imagery date.  Maybe not pretty as the date would have to all be one numeric value now; but this would be the easiest simplest way. At least until they support a more elegant way of storing and accessing raster info in to popups in web viewers. This is still a weak link. DEMs, land use codes, dates for imagery, etc are all examples of useful attributes that are commonly stored as values in a raster pixel.