Quick Web Maps – How’d you do that???


  • As a Geographic Information Systems (GIS) professional for nearly 10 years, I’m used to having people ask, “can you make a map of…”  With the increase in the use of Social Media and the use of web services to share information, it has become much easier to share the data behind the scenes.  Enter in a concept called interoperability.  For many years, the term interoperability was used when two public safety agencies (ie. police and fire) used different radio frequencies and they couldn’t talk to each other.  But as new technology has been developed, interoperability is being used more to describe:

Assembling separate but related pieces of information from different sources and/or disciplines in order to answer a common question

In this morning’s post, October snow and Online Web Maps, I put together a web map showing elevations above 3,500 feet (a snow level discussed my many meteorologists and spotters).  Let’s walk through the separate but related pieces of information and steps to the process to show how they are interoperable with one another to answer the common question “If it snows above 3,500 feet, where will the snow occur?”

  • Identify the question you’re trying to ask.  In our case we’re looking for information on where the snow in higher elevations might occur.
  • Ask what types of data are needed to answer this question?
  • Determine what geographic dataset might be needed (Elevation above 3,500 feet in this case).
  • Locate a dataset or geographic web service  that can be used by GIS software (or one already created online) – in this case we need an elevation dataset.
  • Read the metadata for the file that lets you know the units of measurement
    • The US Topo dataset from NWS was in meters, so the value needed to be converted to feet.
  • Use a Geographic Information Systems software tool (web based or desktop) that can create, modify and symbolize geographic data.  In my case, I’ve used ESRI’s ArcGIS for Home ($100 annual license), but there are other tools out there.
  • Modify or analyze the datasets.  In this case, I needed to convert the USTopo CONUS Elevation dataset from Meters to Feet (3.28′ per meter).
  • Classify your resulting elevation dataset into values to group / simplify what you’re looking at.  In the map below, the elevation is classified every 500 feet.
  • Use a tool similar to ESRI’s Reclassify tool (Using Spatial Analyst – that is included with ArcGIS for Home) to reclassify into categories the
  • If needed, convert file types to one that is useful for online maps.  Here, we converted from Raster data to Vector (Polygon, Point, Line) data.  The ArcGIS tool for Convert Raster to Polygon was used
  • Web mapping data needs to be fast and simple.  Sometimes your raw data is too detailed and needs to be simplified for display purposes.  Here, we don’t want to see individual polygons every 90 meters showing the elevation. Instead, we want to Dissolve the data to simplify it for display purpose

For snow purposes, we want to dissolve only the elevations above 3500 feet.

  • Take a subset of your data that meets a certain criteria (“Elev_Below”>=3500 in our case) and query that out from the generalized polygon data.

Elevations Above 3,500 feet

  • Zoom into the area in question, and export the features shown in the map window (Export View Extent).  This will export to a shapefile the mid-atlantic elevations above 3,500feet.

Export View Extent

  • Log in to ArcGIS Online and click on the “Map” button at the top.
  • In the map, click “Add” and then “Add Layer from file.  You can add in the zipped shapefile that was created earlier.  The resulting map layer will be added, and you can then symbolize the map (in our case, red = elevations above 3500 feet).
  • Look to see if there are other related datasets that might be helpful.  You can add from other users who have shared content via ArcGIS Online or you can add data from the web like Map Services from NOAA’s NOWCOAST service or Iowa State’s IEM Site.
  • Now it’s time to share the map.  A recent addition this month is the ability to Publish the map and have it hosted by ESRI.

Publish Map w/ ArcGIS Online

At the end of the day, this seemed like a long process, but this is where the #EMGIS, #EM, #GIS and #SMEM communties can help.  There are many common datasets that are useful across all these domains.  By sharing content online as web maps and web services, this will enable people to put together the pieces to answer common questions.

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4 comments on “Quick Web Maps – How’d you do that???

  1. Pingback: Is it Possible?? Interactive Wind Forecast Map??? « disastermapping

  2. Pingback: Quick Web Maps – How'd you do that??? « disastermapping | Disaster Mapping | Scoop.it

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