How do I put gridlines on a map?

I know can use the code below(code1) to set the gridlines for this contour plot but I can't get gridlines to show up on the code below that(code2). Code2 shows a few gridlines that correspond to different latitudes and longitudes but I can't figure out how to create different gridlines on it with spacing of my choosing. I tried to do a code similar to code 1 but nothing happened.

CODE 1

figure

contour(XX,YY,ZZ)

grid on

set(gca,'xtick',-30000:500:5000)

set(gca,'ytick',-5000:500:30000)

CODE 2

latlim=[42.7 42.9];

longlim=[-71.05 -70.8];

gravityreading=grav;

figure

usamap(latlim,longlim);

states=shaperead('usastatehi','usegeocoords',true,'Boundingbox',

[-71.05,42.7;-70.8,42.9]);

geoshow(states)

contourm(Y,X,Z,'r')

[c,h]=contourm(Y,X,Z,'r');

ht=clabelm(c,h);

set(ht,'color','b');