CSV（中心点）をインポートして、5kmの円を描く

Yes, you can easily import point data (such as coordinates for a center point) from a CSV (Comma Separated Values) file into QGIS.

The specific tool in QGIS for this task is the “Add Delimited Text Layer” function.

Importing Point Data from CSV

The process requires your CSV file to have at least two columns containing the coordinates (Longitude/X and Latitude/Y).

Step 1: Prepare Your CSV File

Ensure your CSV file is correctly formatted. The headers must clearly distinguish the coordinate fields.

ID	Longitude (X)	Latitude (Y)
1	139.752778	35.684444
2	139.691700	35.689500

Step 2: Use the “Add Delimited Text Layer” Tool

1. Go to the Layer menu $\rightarrow$ Add Layer $\rightarrow$ Add Delimited Text Layer…
2. In the dialog box that appears:
   • File Name: Browse to and select your .csv file.
   • Record and Fields Options: Ensure the correct delimiter (usually Comma) is detected.
   • Geometry Definition: Select Point coordinates.
     • X field: Select the column header that contains the Longitude or Eastings value (e.g., Longitude (X)).
     • Y field: Select the column header that contains the Latitude or Northings value (e.g., Latitude (Y)).
   • Geometry CRS (Coordinate Reference System):
     • If your coordinates are standard Latitude and Longitude, set this to EPSG:4326 - WGS 84.
     • If your coordinates are in a projected system (meters/feet), select the appropriate CRS.
3. Click Add.

円（5km (5000m)）を描く

一旦、座標系（CRS）を変更（4326->3857）してから、円を描いた。degree単位をkmに変更するため。

地理情報システム（GRS）を変更する

Drawing 5km Circles (Buffers) Around Imported Points

Step 1: Open the Buffer Tool

1. Go to the Processing menu $\rightarrow$ Toolbox.
2. In the search bar of the Processing Toolbox, type “Buffer“.
3. Double-click on the Buffer tool (found under Vector Geometry).

Step 2: Configure the Buffer Parameters

In the Buffer dialog box, set the parameters as follows to ensure accurate 5km circles:

Parameter	Setting	Notes
Input layer	Select the name of the layer you imported from the CSV file (e.g., center_point).	This is the layer containing all your center points.
Distance	Enter the number: 5	This is the radius value.
Distance unit	Select: Kilometers	Crucial: Setting the unit here tells QGIS exactly how far to calculate the buffer.
Segments	5 (Default) or a higher number (e.g., 10 or 15)	This controls the smoothness of the circle’s edge. A higher number yields a smoother circle.
Dissolve result	Do not dissolve buffers (Uncheck/Default)	Unless you want overlapping 5km circles to merge into one single area, keep this unchecked.
Buffered	Click the … button and choose Save to File...	Give the new layer a meaningful name (e.g., 5km_service_areas.gpkg).

Step 3: Run the Tool and View Results

1. Click the Run button.
2. QGIS will process the input layer, internally use an appropriate distance-preserving Coordinate Reference System (CRS) for accurate calculation, and generate a new polygon layer containing all the 5km circles.

The new layer will appear on your map canvas, showing a perfect 5km radius circle around every point you imported from the CSV file.

円が描けた！