I am a GIS newbie. I'm having a problem that, from the looks of things on this website, is a fairly common problem. I have 3 layers, all in the same GCS that do not line up. I have read all the the strings that others have posted on this website regarding this kind of problem, but I still haven't been able to figure out how to fix my particular issue. I am just a social studies student, trying to do a project. I don't have GIS training, so I feel very lost at sea, with all the complex technical terminology.
Here are the details:
I am working with data for the City of Chicago, USA. I have a street map for Chicago (chicagostreets1999, derived, I think from the US Census), a map of census tracts for the year 2000 (tracts2000, from the US census), and a zoning map (Zoning_nov2012, provided online by the Chicagy City Hall).
Census tract boundaries run along streets. The tract boundaries in tracts2000 line up nicely with the street map from chicagostreets1999. Zoning boundaries also follow streets, but the zoning map does not line up properly with these two other files. When I compare the zoning map to the street file, its lines are about 175 feet (53 meters) south, and 148 feet (45 meters) east of the relevant lines on the street map.
I looked at the "source" information on each file in arcGIS. Here is the info on their Geographic Coordination Systems.
Tracts 2000***** Data Type: Shapefile Feature Class Geometry Type: Polygon
Geographic Coordinate System: GCS_North_American_1983 Datum: D_North_American_1983 Prime Meridian: Greenwich Angular Unit: Degree ![Misalignment, zoom in][1\
*Chicago streets 1999****
Data Type: Shapefile Feature Class Geometry Type: Line
Geographic Coordinate System: GCS_North_American_1983 Datum: D_North_American_1983 Prime Meridian: Greenwich Angular Unit: Degree
**Zoning_nov2012*******************
Data Type: Shapefile Feature Class Geometry Type: Polygon
Projected Coordinate System:
NAD_1983_StatePlane_Illinois_East_FIPS_1201_Feet Projection: Transverse_Mercator False_Easting: 984250.00000000 False_Northing: 0.00000000 Central_Meridian: -88.33333333 Scale_Factor: 0.99997500 Latitude_Of_Origin: 36.66666667 Linear Unit: Foot_US
Geographic Coordinate System: GCS_North_American_1983 Datum: D_North_American_1983 Prime Meridian: Greenwich Angular Unit: Degree
I tried setting the coordinate system for all three files by double clicking the "Layer" meta-category in the data view window, and then selecting "Coordinate System" within the data frame properties window. The coordinate system was already defined as:
*Layers**** NAD_1983_StatePlane_Illinois_East_FIPS_1201_Feet Projection: Transverse_Mercator False_Easting: 984250.000000 False_Northing: 0.000000 Central_Meridian: -88.333333 Scale_Factor: 0.999975 Latitude_Of_Origin: 36.666667 Linear Unit: Foot_US
GCS_North_American_1983 Datum: D_North_American_1983
This seemed to be the same as all three layers, so I did not change it.
I asked the GIS librarian at my university what the problem might be and what, if anything could be done, to fix the misalignment. He said that he did not know how to fix it, and that the problem was probably due to the City Hall GIS people scanning in their zoning map "at a different scale" than the Census people did. I don't know whether that is true, but I really would like to get these files to align properly with each other. It will make the process of analysis a lot easier (ie not horribly visually confusing), and also more accurate.
I am happy to share the files in question with anyone who might be able to help. The Zoning data, for instance, is freely available here on the City of Chicago's City Hall government website:
https://data.cityofchicago.org/Community-Economic-Development/Boundaries-Zoning-Districts/p8va-airx
I can email the street file to anyone who is willing to help.
Thanks so much for your advice!
