A ‘Unknown Spatial Reference’ means there’s a datum conflict.In this case, ‘unknown units’ will appear in the bottom right corner of Arc Map and you should use the Define Projection tool.
There are solutions for practically EVERY GIS problem.
Free integration with R stats (Geospatial Modelling Environment), Marine Tools add-on, Net CDF interoperability, ET Geo Wizards, Arc GIS Patch Analyst,…With Esri’s latest addition for an app store of their own – Arc GIS Marketplace, even more plugins will be rolling out like clockwork.
Whether it’s simple math (map algebra and conditional toolset), statistics (multivariate, neighborhood or zonal toolsets), or generating value surfaces (interpolation, density or overlays), Arc GIS raster-based tools are rock-solid.
The Spatial Analysis tools also offers specialized tools for groundwater, hydrology, cost surfaces and solar radiation.
The bottom line is that Arc GIS Online (AGOL) is a rich source of GIS data. An advanced license gives you access to everything.