Beginner - hotspot analysis

[ClaireMarshall]

Hello!

I'm hoping this is a straightforward question to answer!

I am trying to do a hotspot analysis for a dataset of road accidents. I am using the OpenStreetMap as a basemap, and originally imported my dataset with the geographic coordinate system WGS 1984. However when I tried to perform hotspot analysis, it didn't work and told me that "the input feature class does not appear to contain projected data". So, I imported my data again using the projected coordinate system, World>WGS1984 Web Mercator (I didn't know which WGS 1984 to choose, there were a few!). However my data points now show that they are in Nigeria, not Scotland!

If anyone could help I would appreciate it so much, it is for my dissertation and I've been trying to figure out how to use hotspot analysis for months!

Kind regards,

Claire

p.s. I'm using ArcMap 10

[KishorGhatage]

Could you please let me know which method you used to reprojcet the point dataset?

Please use Project tool (Data Management) to re project your point data in projected coordinate system(WGS1984 Web Mercator / UTM) and then use Hotspot analysis.

[RussellHooper]

Hi Claire,

as your accident data is in Scotland I suspect the the coordinates will be in British National Grid coordinate system, but this information has probably not been provided to your accident feature class. I've tried for one point in Scotland and if I don't define the projection to British National Grid, my point appears off the coast of Nigeria (using OpenStreetMap). Your problem is that the Data Frame is in in one coord system and your data in another, and ArcMap doesn't know the correct coord system of your data

I suggest using the "Define Projection" tool to set the spatial reference of the accident data to British National Grid.

When you add the accident data to ArcMap, you may then be get a warning and a request to transform the data so it displays correctly with the OSM map. Accept the request and convert from GCS_OSGB_1936 to CCS_WGS_84 using the ..."Petroleum" transformation recommended by ArcMap. If your at Uni I thought you would have access to OS backdrop maps that will be in the OS projection, and would allow you to avoid transformations.; would be worth checking.

Good luck,

Russell