Overlaying rectangular polygon grid to extract tiled map subsets?

by scifijensfly   Last Updated November 28, 2017 09:22 AM

I want to be able to create/extract subsets(or tiles) of map data to new layers so that I can export them as tileable jpegs. The tiling is important for my project. My strategy is to place a grid of rectangle Polygons on individual layers and use them to extract map subsets from an underlying Shapefile.

When I create a new project the CRS is set to WGS-84 EPSG-4326.

I have an underlying map - a Shapefile of building plots - when I import it, its CRS is set to CRS(EPSG:4326, WGS 84). My area is in Malmö, Sweden.

I then use the plugin quickWKT and paste a WKT file of a set of polygons: the file looks like this:

POLYGON((1449008 6180085,1449008 6163387,1414376 6163387,1414376 6180085,1449008 6180085))

etc etc...

(I have 9 polygons, 3x3).

The new layer created from these polygons is a shapefile layer (I think) and has same CRS as the project CRS and underlying layer. Now from what I understand, the coordinates used for these polygons are system RT90 and not WGS. The polygons do not map onto my underlying layer of house plots. They are far off in the distance.

Can anyone help me in a direction?

Answers 1

Since the projections of the two files are different, you need to unify the projection. If I understand you well, you do not want to use WGS 84 but you want to use RT90 projection. If this is correct, you need to reproject your point data by right-click the layer in the table of content -> Save as:

enter image description here

  • Click on CRS icon to select the proper RT90 projection.
  • Write RT90 in the Filter area, and you will get a list of projections that use RT90
  • You need to choose the correct one that matches the polygon grid
  • Save the output point into a new file (shapefile or any other format that you want)
  • Load both point data and polygon grid into a new QGIS project. If the projection is correct for both files, they should overlay each other.
November 28, 2017 09:19 AM

Related Questions

Issues with projection system in R (raster package)

Updated November 16, 2017 18:22 PM

Transforming coordinates in R?

Updated July 26, 2017 10:22 AM

Polygons intersection with WGS84 coordinates

Updated January 15, 2018 17:22 PM