Importing from Excel/CSV format to QGIS

Question

I created a grid and used it's squares and it has 4 values in attribute table (each square has left, top, bottom, and right values). Every square is a different object. I try to export file from Excel/CSV, while importing in QGIS, its shows points coordinates X filed, Y field and I have (left, top, right, bottom values) 4 points to make it grid (square).

How do I import correctly in QGIS from Excel/CSV?

Answer 1

You can create a virtual layer from the information in the excel file.

Add the excel or csv file to the map, and MakePolygon using the four corner coordinates:

select MakePolygon( 
 GeomFromText(concat('LINESTRING(',
 "left",' ',"top",
 ',',
 "left",' ',"bottom",
 ',',
 "right",' ',"bottom",
 ',',
 "right",' ',"top",
 ',',
 "left",' ',"top",
 ')'))
 ) as geometry, *
from gridexport

Replace gridexport with your table name and set the crs in the dialogue:

enter image description here

Answer 2

Either convert your coordinates to WellKnownText format, or change the layout of your table so each corner of each square has its own row, including a square ID, a point ID and its X and Y coordinates. Duplicate the first point of each square and add it as the fifth.

Your table should look as follows:

Square ID	Point ID	x	y
1	1	0	0
1	2	1	0
1	3	1	1
1	4	0	1
1	5	0	0
2	1	10	10

Then load your csv into QGIS, run points to path and finally convert your lines to polygons.

Answer 3

In MSExcel fill in columns A to H the corner coordinates, in column I the id that identifies the polygon, create in column J field geom, calculate geom with the following formula:

="POLYGON(("&A2&" "&B2&", "&C2&" "&D2&", "&E2&" "&F2&", "&G2&" "&H2&", "&A2&" "&B2&"))"
LLx LLy LRx LRy URx URy ULx ULy id geom
-2300 -1000 -1400 -1000 -1400 -400 -2300 -400 block1 POLYGON((-2300 -1000, -1400 -1000, -1400 -400, -2300 -400, -2300 -1000))
-1400 -1000 -500 -1000 -500 -400 -1400 -400 block2 POLYGON((-1400 -1000, -500 -1000, -500 -400, -1400 -400, -1400 -1000))

Save as TABseparated textfile, and import as WKT in QGIS: Layer > Add layer > add delimited text layer...

Add your exported text file, select File Format: custom delimiters tab, Geometry Definition: Well Known Text, Geometry Field geom and click add.

Answer 4

Besides the numerous solutions proposed, you could use the Geometry Generator to create the polygons.

If your CSV-file has the following form:

xmin,ymin,xmax,ymax
-0.5,-0.5,0.5,0.5
-2,-1,1,2
...

you can load it using QGIS' CSV driver (Select xmin and ymin for xy): enter image description here

Then change the "Simple Marker" styling to "Geometry Generator (Polygon/Multipolygon" and use the following expression to generate your polygons:

 geom_from_wkt( 'POLYGON((' ||
 "xmin"||' '||"ymin"||','||
 "xmax"||' '||"ymin"||','||
 "xmax"||' '||"ymax"||','||
 "xmin"||' '||"ymax"||','||
 "xmin"||' '||"ymin"||','||'))')

With the processiong tool "Geometry by expression" you can save the geometries into a spatial layer.