We live in Stevenage, Hertfordshire and aware that there is no grammar/good secondary schools in Hertfordshire. My DS is in yr 3.Iam not very good at geography either. So iam finding it very difficult to make up mind on which schools to make him write exams for and which area would be best for us to move if he has to get into good secondary school. I did read a lot in this forum and came to conclusion that qe boys would be our only choice. We really don't want to move to any other area before he gets admission to any grammar school but happy to move if there is a bit of guarantee that he will get a space .The other school we are interested is DAO, SW CONSORTIUM schools,Latymer.Need some guidance on which area to move if needed so that he can sit for exams in most schools and some advise about schools which he can write first and move to the area once he get a place.

Are you sure your current options are not suitable? I did a quick look at Stevenage secondaries - Marriotts is rated Good, John Henry Newman is Good (but catholic, not sure whether it admits non-Catholic children), Nobel is Good, Thomas Alleyne is Good.

If you do decide to move, you will not know for certain which school you have been allocated until 1 March at the earliest. That will give you six months or so to relocate before the start of the school year. Will that be enough time?

You can sit entrance exams for all schools without having to live in the catchment for the schools. Most of QE's places are open so they allocate places based only on test results. So you can sit the exam for that school from your current location and move after the places are given on 1 March.

However, for some schools (I think DAO and Latymer fall into this category but others will confirm) you need to be living near the schools at the time of submitting the CAF (end of October) or shortly thereafter in order to stand a chance of getting a place. Obviously if you move to be near the schools and then don't get a place you need to be sure that your fallback options are OK as well.

Before you think about moving your family to be eligible for places at these schools, do actually go and visit them. The schools you've named are all excellent schools but not all of them will be right for your DS (they are very different in character). Also visit your current local schools so that you can make an informed comparison before you commit to moving.

I suggest you look again because that simply isn't true. streathammum has listed four good schools in just one town. You are mistaken if you think that only grammar schools are good schools. Do you really think that all Hertfordshire children are attending secondary schools that aren't good? Have a look on Ofsted's web page to read some of the reports for the schools. They might reassure you that there are good schools in your area.

My ds plays a sport with a child from Nobel school in Stevenage.
His parents are delighted with the school. By all accounts this child is "gifted" and he is stretched and encouraged and attends a lot of events designed to stretch the most able.
Maybe go on some open evenings or go to a summer fete and get an idea of your local schools before looking to move?
To answer your specific question I don't think that you can live anywhere and apply for all the schools you've mentioned. You can live in Borehamwood and apply for DAO and SW consortium (and for the Latymer test but would have to move after results to get a place) but I don't think the area of overlap is particularly big.

I can't imagine wanting to live in Stevenage, either (sorry ), but surely there must be something that attracted you to the town in the first place? Is your DS's primary school awful, as well? If there are good primary schools, it's unlikely that all the secondary schools are bad. Or does everyone who can afford to send their DC to an independent school at the age of 11? As you say, there are no grammar schools to cream off the top of the ability range.

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I know that there used to be parts of North Stevenage that really struggled to be in catchment of any of the secondary schools; so this may still well be the case. OP look at the admissions criteria for all the schools that you are potentially interested in and that will give you all the information you need about catchment/when you need to be living in an area direct from the source.

Very sweeping statement to make. I have friends in Herts whose children are at excellent schools and they are thriving.

I'm guessing that The OP actually means they are only interested in grammar schools,that is certainly how it reads to me. Interestingly, I'm also assuming OP is not speaking English as a 1st language, so perhaps there may be a language barrier/misinterpretation...
Perhaps more interestingly there have been numerous posts over the years where those with ENFL are happy to move wherever to get a grammar place so is this perhaps a cultural thing?
Just looking for reasons behind the apparently 'closed view'

Culture and language aside, there is certainly a percentage of the general population that suffer from the misconception that grammar schools are the only good schools, and a sub-set of those are seemingly prepared to up sticks, move family anywhere and make their children sit multiple tests in the pursuit of a place at one. Hertfordshire is the latest area to supposedly not have any good schools. In recent months I have challenged other posters who insisted that there are no good schools in Luton or Basingstoke, when a cursory glance at Ofsted reports and school performance data emphatically proved them wrong.

I do wonder whether that government's £50m they've found down the back of the sofa for grammar school expansion might be sensibly spent simply re-branding hundreds of upper and comprehensive schools as grammars, to satisfy the parents whose research into suitable schools seems to rely solely on the inclusion of the word in the name.

Back to the OP's situation, I urge you to look more carefully into your local options. If none of them are suitable then look elsewhere but rule out Bucks if you want a school where you can move after knowing the result and still get a place.

But if you will only consider a grammar school as 'good', Stevenage seems an odd place to choose to live? Hence my assumption that there must once have been other, more compelling, reasons than education to be there in the first place.

Interesting history of the former grammar schools (amongst other educational establishments) here, though:
http://www.ourstevenage.org.uk/content/category/topics/schools-and-education

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Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read.Groucho Marx