3D Gravity plot problem - how to differentiate between separate sections of a vector?

Hi, I am trying to plot a 3D topography profile using gravity data.

I have three vectors: x-coordinates, y-coordinates, topography values.

I have used meshgrid and TriScatteredInterp to generate a a plot but it is messy and I think the reason for this is that I have data for 7 separate survey lines, i.e. the data was collected in 7 straight lines forming a grid.

...so when i have data for 7 lines 'lined up on top of eachother', it interpolates between the beginning of one survey line and the end of another etc.

How do i get MatLab to recognise the 7 separate lines whilst still being able to use meshgrid etc, with 3 vectors to describe x-coord, y-coord and topography data?

Here's my code:

load ne_top_lines_zgrav.txt

E = ne_top_lines_zgrav(:,2);
N = ne_top_lines_zgrav(:,1);
grav = ne_top_lines_zgrav(:,3);

F = TriScatteredInterp(E, N, grav);

[x, y] = meshgrid(E, N);

z= F(x,y);

hold on
surf(x,y,z);

Really appreciate your help!