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I have been struggling with this simple problem all day. I found a Florida map with the counties on Google for GIS. I uploaded the map to QGIS with no problem. However, whenever I try to upload points (both latitude/longitude and x,y coordinates) of areas in Florida, the points do not line up with the map. I have tried different coordinates and I have experimented with the CRS of the maps and I have lined everything up with the same references, but I still have no luck. Has anyone ever tried to do this before?

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    What are the projections of the counties data and points data? – ahmadhanb Apr 20 '16 at 2:59
  • note that you should enter the degree coordinates in longitude-latitude order, with negative (Eastern) values for longitudes in the United States.. – AndreJ Apr 20 '16 at 5:22
  • The projections of both is EPSG 2237, NAD 83/ Florida West (ftUS). – Anne Apr 20 '16 at 14:01
  • I entered the degree coordinates in the longitude-latitude order, but the points would always appear under the Florida map. They appeared in a similar place if I changed it to x and y coordinates. – Anne Apr 20 '16 at 14:03
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looks like you know the projection of your map, but perhaps it is wrong; it is best to just treat it as an unknown projection, and convert it to a known projection using the Georeferencer plugin

http://docs.qgis.org/1.8/ro/docs/user_manual/plugins/plugins_georeferencer.html

Georeferencer Plugin:

The Georeferencer Plugin is a tool for generating world files for rasters. It allows you to reference rasters to geographic or projected coordinate systems by creating a new GeoTiff or by adding a world file to the existing image. The basic approach to georeferencing a raster is to locate points on the raster for which you can accurately determine their coordinates.

how to georeference a plain image map

qgis

Plugins->Manage Install Plugins

[X] Georeferencer GDAL <-make sure it is checked then click [close]

right-click on the toolbar and make sure [X] Raster is checked

click on the Georeferencer icon which might look like a # sign in the toolbar that appears when checking Raster above;

a new window appears

File menu, open a plain image map;

click the add point icon in the toolbar then click on map and add lon,lat coord pairs for several well known points by checking with google maps for example recognizable features; points should be spaced throughout the image not just in one place; 15 points for example is sufficient; the minimum is 6 points;

points can be saved in text file using File->Save GCP points as... each point is saved as lon,lat,x,y,1 pair where x,y is the pixel coord in the input not the output image; origin is at top left; x increases to right; y decreases downward;

Settings->Transformation settings

Transformation type: Polynomial 2 (most used)

Output raster: out.tif (output name should be put here - output will be geotiff regardless of filename)

Target SRS: EPSG:4326 (this is a good projection - size of 1 lon = 1 lat throughout the map, used to texture a sphere)

[X] Load in QGIS when done

click [OK]

click green triangle play button to run conversion

File->Generate GDAL script to show how to do this particular conversion at command line - there will be 2 commands, a gdal_translate and a gdalwarp; note that the gdal_translate command will not have -a_srs EPSG:4326 option - this option has to be manually added to the command; that is all.

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