Smith-9th Street View Shed Again: But this time with ARCGIS On-Line

   ARCGIS ESRI has a on line service that although you have to pay for it, has  many interesting features.  One of those that I stumbled across is their analysis section is that of viewshed analysis.  Will the object in question be visible, let us say a power windmill 9 miles away?  How tall shall we make a windmill so less people will object?  How about the Smith-9th Street station, the highest in the NYC subway system?  I used GRASS to calculate this before, but it is cumbersome: You need an X and Y coordinate and getting the resultant map in the proper format is hard.  In ARCGIS on line, you can go to the analytic section and locate Viewshed.  Pan the base map that you choose to the location that you want.  You can use a pointer to add the point of interest.  Add the height of the object, this time the Smith-9th street subway station.  You can get the location by bringing in a NYC subway stop shape file that you need to zip.  The second height is that of the observer.  In the first map above,  I used the default value of either 0 or 6 feet, the size of a person.  You can add a range.  In the second map, I ran the analysis but I added that a ground viewer would be on a 40 foot building.    The results of the first and second analysis is shown on the joint map above.  Being on a higher location will result in a larger range.  In Manhatan, very high buildings will block your view and you will not be able to see the Smith-9th Street station.  The reverse of this analysis is also true:
"If I am at the Smith-9th Street Station, what can I see?"  If the city consisted of 40 foot buildings, the map above is what you can see.  Check out ARCGIS on line if you have an account or if you have a free one.
Tramway Null