Add formula for resolution to Chapter 5 about geocompr HOT 2 CLOSED

While reading 5.3.3, I took the following notes to resolve the issue I was having with the resolution:

Let's review the changes from dem to dem_lower:

Notice that "decreasing" the resolution with aggregate() actually increases the component values of the resolution in the raster header from $(30.85, 30.85)$ to $(154.25, 154.25)$. This is counterintuitive, but it helps to the review the formula for the resolution per the raster data model.

$\displaystyle \text{resolution} = \Big(\frac{\text{xmax} - \text{xmin}}{\text{ncol}}, \frac{\text{ymax} - \text{ymin}}{\text{nrow}}\Big)$

aggregate() "decreased" the resolution by decreasing the grid size, that is, by decreasing the number of rows (nrow) and columns (ncol). The extent was slightly adjusted probably to accommodate the new grid size. Decreasing the number of rows and columns, in turn, actually increases the component values of the resolution per the formula.

from geocompr.

@tibbles-and-tribbles thank you.

Please take a look at my changes at #1043.

I move the equation to the second chapter (as it is a general concept), and added some of your explanation to the fifth chapter.

from geocompr.