# maps and isolines on the map of the continents

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ELISABETTA BILLOTTA on 24 Jul 2021
Answered: darova on 25 Jul 2021
after having visualized the boundaries of the continents in the form of a map, I would like to create isolines within this map which identify and connect points with the same characteristics to each other. example: considering Naples as the center, I would like to create a line that connects the points that are located at a distance of 100 km from Naples, but only those on the continents not on the sea. an example would be lines 1-2-3, etc. in this figure
how can I do? ##### 2 CommentsShowHide 1 older comment
ELISABETTA BILLOTTA on 25 Jul 2021
I calculated the data to create the isolines .. they are a simple Excel table with latitude, longitude of the point and value at that point.
I thought about contour but I don't know how to enter the data.

darova on 25 Jul 2021
t = 0:0.02:2*pi; % angle
r = 1 + 0.1*cos(10*t); % radius
[x0,y0] = pol2cart(t,r); % calculate cartesian coordinates
u0 = diff(x0); % component of x tangent vector
v0 = diff(y0); % component of y tangent vetor
u1 = u0./hypot(u0,v0); % normlizing
v1 = v0./hypot(u0,v0); % normalazing
u1(end+1) = u1(end); % copy last value (to make the size as 'X')
v1(end+1) = v1(end); % copy last value (to make the size as 'X')
x1 = x0 + 0.3*v1; % equidistant curve
y1 = y0 - 0.3*u1; % equidistan curve
plot(x0,y0,'r')
line(x1,y1)
legend('Original curve','equidistant curve') 