How much nessesary is a site map

is a sitemap really necessary for a website and why? How can build a site map? Is there any special tool for that job? I am new year and I don;t know basic things about the inner mechanisms of a website and the way spiders look at it.
Thank you in advance

 

I have used sitemaps in all guises in the past, It's always good to have some sort of sitemap to allow the spiders to index your page easier, however it does not guarantee listings or better placement. Google sitemaps I have found aren't all that useful but you do get access to some good info through google webmaster tools so there's nothing to lose. Yahoo sitemaps are very useful and will help your site get indexed much quicker than without one.

www.google.com/webmasters/sitemaps/

 

It may sound slightly odd to ask but are there any known downsides and problems experienced from using a sitemap where one was not previously in place?

 

Yes people have said they had problems using Google sitemaps - see http://forums.digitalpoint.com/showthread.php?t=100844

 

Thanks turfsniffer, il check it out

 

I submitted a sitemap for one of my sites and I lost all my rankings (dropped from positions 5-10 to 500-5000) and and 90% of my indexed pages were removed.

 

Someone said it's not good to add sitemaps...

 

Im definately not going to risk using a sitemap now after reading what happend to you and quite a few other people DLGx, thats terrible, im sorry that that happend to your site hope your site is getting back to normal after that?


Richie_Ni, i agree, it definately doesn't seem good at all.

 

There has been no change since it happened, my highest earning site too, lost more than half its traffic.

 

DLGx, I hope your site recovers before too much longer, especially as you mentioned it was your highest earner too.

 

Sitemap, is not a compulsory stuff to have but it's optional if you have it's good if you don't have it doesn't count negative on you.

The core advantage one will get by using google site map is:-

1-Query stats and their position
2-When did google access your site last time
3-Any error if reported.
4-An option to resubmit site for crawl.
5-An option to set faster crawl rate.
6-Number of pages submitted.

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Reputation appreciated

 

Sitemaps has done nothing as far as changing my rankings in G. If you have links to all your content and external sites link to your site, all your pages will be picked up in G regardless of whether you have sitemaps or not.