You need to get the iframe code from google maps and hen copy the “src” attribute url and put it in your shortcode.
For example if your iframe is :
<iframe marginheight="0" scrolling="no" src="http://maps.google.com/maps?q=897+West+Broad+St.+Columbus,+OH.+43222&ie=UTF8&hq=&hnear=897+W+Broad+St,+Columbus,+Ohio+43222&gl=us&ll=39.958996,-83.024507&spn=0.009095,0.021136&t=m&z=14&vpsrc=0&output=embed" marginwidth="0" frameborder="0" height="350" width="425"></iframe><br /><small><a href="http://maps.google.com/maps?q=897+West+Broad+St.+Columbus,+OH.+43222&ie=UTF8&hq=&hnear=897+W+Broad+St,+Columbus,+Ohio+43222&gl=us&ll=39.958996,-83.024507&spn=0.009095,0.021136&t=m&z=14&vpsrc=0&source=embed" style="color:#0000FF;text-align:left">View Larger Map</a></small>
You should copy this part only :
http://maps.google.com/maps?q=897+West+Broad+St.+Columbus,+OH.+43222&ie=UTF8&hq=&hnear=897+W+Broad+St,+Columbus,+Ohio+43222&gl=us&ll=39.958996,-83.024507&spn=0.009095,0.021136&t=m&z=14&vpsrc=0&output=embed