How do I make an array of gps coordinates over land?

Question

I am writing a python algorithm, which optimizes telescope positions for a radio interferometers, and for this i need an array of gps coordinates for possible positions to choose from. For now I have been using a big grid covering the an area of interest (see image).

Image

However, the problem is that I would like to avoid the positions over water/oceans and only have a grid of evenly spaced coordinates over land. Any ideas of how I can achieve this? I know there is data for similar stuff here:

https://freegisdata.rtwilson.com/ https://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html

The code I have below works fine and produces a grid over the globe just fine. I am just looking for advice on the above mentioned goal:

import matplotlib.pyplot as plt
import numpy as np
import random as rand
from mpl_toolkits.basemap import Basemap

upper_lat = 70
lower_lat = -70
upper_lon = 140
lower_lon = -140

size = 100


#initializing which gps coordinates to start at 
La = lower_lat
Lo = lower_lon

#array to store coordinate
sites_gps = np.zeros((size*size,2))

f=0
for j in range(0,size):
    Lo=lower_lon
    for k in range(0,size):
        sites_gps[f] = La, Lo
        Lo+=(upper_lon+abs(lower_lon))/size
        f+=1
    La+=(upper_lat+abs(lower_lat))/(size)