How to determine the projection or coordinate reference system given spatial points

Question

I am just a starter to Spatial Analysis and am stuck at a point.

I have a crime data set where the points are given in latitude and longitude. I have another dataset (a shape file of Chicago) and I would like to plot all the lat-long points on top of map plot using the polygons from the shape file.

The problem is that the shape file contains polygon information in a different format which I am unaware of. I retrieve the shape file from
https://data.cityofchicago.org/Facilities-Geographic-Boundaries/Boundaries-Neighborhoods/9wp7-iasj

From the above download I use the Neighborhoods_2012b.shp file

Latitude Longitude from crime data:

POINT (-87.680162979 41.998718085)
POINT (-87.746717696 41.934629749)

Polygon shapes in the Chicago Shapefile: (All are positive values)

POLYGON ((1182322.0429 1876674.730700001, 1182...
POLYGON ((1176452.803199999 1897600.927599996,...

I tried transforming the Latitude and Longitude information into different projection (Mercator) such as (epsg:3857, epsg:3395), but these projection give me both positive and Negative values

epsg:3857:
POINT (-9760511.095493518 5160787.421333898)
POINT (-9767919.932699846 5151192.321624438)

I even tried transforming all Lat-Long into UTM (using the python UTM library), which hopefully gives me all positive value but still it doesn't seem the right format as the plots are at very different scale.

Using UTM python Library (utm.from_latlon)
POINT (4649857.621612935 443669.2483944244)
POINT (4642787.870839979 438095.1726599361)

I am not sure how to handle this situation, Is there a way to know what type of projection is used given the spatial points?

I'd be glad for any help.

I tried reading the Chicago shapefile, I am getting negative values in polygons such as - ` "geometry": {"type": "Polygon", "coordinates": [[[-87.6067081256125, 41.81681377057218], [-87.60670480954393, 41.81657908503414],...]]`. Is it the same file you posted above? — Amey Dahale
Hi Amey, I am really sorry about the dataset, I have changed the URL in my post. After downloading the Neighborhood data I use the Neighborhood2012b.shp file. — Sam

Sébastien Rochette Sébastien Rochette · Accepted Answer · 2017-05-30T19:26:41

The prj file says:

PROJCS["NAD_1983_StatePlane_Illinois_East_FIPS_1201_Feet",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",984250.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-88.33333333333333],PARAMETER["Scale_Factor",0.999975],PARAMETER["Latitude_Of_Origin",36.66666666666666],UNIT["Foot_US",0.3048006096012192]]

I opened the layer with QGIS and it did not use the prj file directly. However, with the information of the prj file, you can use the CRS selector to retrieve it. Search parameters are : NAD83 Illinois East here. Choose the one that is in Feet as suggested by the prj file. EPSG = 6455 is a good one for instance. I think you now have enough information to continue...

How to determine the projection or coordinate reference system given spatial points

1 Answers