2.1. Loading a table and converting to a point layer

In this section, we will be handling point data from an Excel table. and converting it to a point layer. Finally, we will interpolate the point layer to obtain the precipitation in our Hadocha watershed. One interesting aspect is that the coordinates of the weather stations are in a different Coordinate Reference System (CRS) than the rest of our data, and we will have to reproject them.

2.1.1. Follow Along: Loading and selecting the table data

First, we have to load the data.

1. In the Browser pane, find GIS_files ► data ► rainfall.xlsx. This is the rainfall file we will be using. Load it into the project and Open Attribute Table.

   You are looking at processed data from NCEI. They provide measured data from weather stations on the world. However, not al years had data for all months. For each station, the precipitation was summed for all years that had 12 months of data. Then, the average was taken over these years. As you can see, not all stations have data for a sufficient number of years.

2. Why is this a problem? What do you think is an acceptable number of years?

   Solution and steps

   We think an acceptable amount of years is 5 for this case. Ideally, we would want at least 10 years, but given the available data, we found that more stations outweighed more years. Now, we will select the stations that have \(years \geq 5\) years of data.

   1. In the processing toolbox, look for Vector selection ► Extract by attribute. and fill it in like so:

      

   2. optionally, make the new layer permanent

2.1.2. Follow Along: Converting to a point layer and reprojecting

1. To find out where our points end up, we want to see where we are on the earth. For that, we will load the OpenStreetMap basemap under XYZ Tiles in the Browser.

2. Find the Create point layer from table algorithm.

   1. Set the Extracted (attribute) layer as Input layer

   2. Set X field to LONGITUDE

   3. Set Y field to LATITUDE

   4. Leave the Target CRS on EPSG:4326 - WGS84. This is the CRS that our table data is in. We do not have an option to reproject now and will do that in the next step.

   You should get the following points:

   

   If they are on a different location on the world, check your settings!

3. Find the Reproject layer tool.

   1. select Points from table [EPSG:4326] as Input Layer

   2. As Target CRS, set UTM zone 37N

      Your new layer Reprojected should be exactly on top of the old layer.

4. Optionally, make the layer permanent.