When I was looking for info on converting latitude/longitude to $(x,y)$ Cartesian coordinates, I found this link on Doctor Math.
I found this following formula:
In Radians: $$x = (\text{lon}_2 - \text{lon}_1)\times \cos(\text{lat}_1)\times \frac{\pi}{180}$$ $$y = (\text{lat}_2-\text{lat}_1)\times \frac{\pi}{180}$$
In miles: $$x = (\text{lon}_2-\text{lon}_1)\times \cos(\text{lat}_1)\times \frac{\pi \times R}{180}$$ $$y = (\text{lat}_2-\text{lat}_1)\times \frac{\pi\times R}{180}$$
And :
$$\text{lat}_2 = \text{lat}_1 + y\times \frac{180}{\pi\times R}$$ $$\text{lon}_2 = \text{lon}_1 + x\times \frac{180}{\pi\times R\times \cos(\text{lat}_1)}$$
The Question:
Why converting to radian or degree for finding x,y?
Are there any references that explain the previous conversion formula?
Thank you :)