For the places mentioned in my family history I'm looking to make sure I have the native spelling correct. The problem is that many events' places no longer exist. Some places (like Prussia) are not much of a problem but there are other locations (e.g., Spilleren Farm, Meløy, Norway in 1782) where I don't even know where to begin.
Although I can't be certain 100% (especially as events date further back in history) how do I get reasonable confidence in an ancient location's spelling?
The best answer to this will vary with geography, but I'll make a few suggestions:
The spelling will almost certainly vary with time and with the language of the person referring to the place, and with the individual making the record. You have to resign yourself to the fact that there isn't a single correct spelling.
I try to refer to old maps or gazetteers to get a contemporaneous 'official' spelling. (Of course this is easier in some places than others.) So I would start by looking for old maps of Norway in your search for Spilleren Farm, Meløy, Norway.
Other contemporaneous documents (e.g. censuses or parish registers) may give you an idea of what was most commonly used. FamilySearch may give you a start on your Norwegian location.
Spellings didn't use to be standardized, so you can't confirm the "proper" ancient spelling, because there isn't one. If the place still exists then there is a proper modern spelling, and using that in your documentation is usually preferred.
When the place doesn't exist anymore then simply using the most common ancient spelling is OK.
In all cases, if the mapping between the spelling as used in the sources and the modern spelling that is used is non-obvious, using both is recommended. When referencing a source you can often include a quote, so you can enter somebody as born in, say, Wrocław, and note in the source for the reference that the source says "Breslau", for example.
Until we have a property 'Place Authority' that can help with spelling variations, name changes, names in different languages, boundary changes, local history, etc., you're going to have to rely on your own research.
I would strongly recommend centralising your data for each place (assuming your software supports that concept) so that you only have one entity representing a given place - no matter how many times it is referenced from different events. That simplies maintenance, including any additions or corrections you may have to make to it afterwards.
I guess the answer to this depends on the location (country), but you gave Norway as an example here.
In Norway there is actually a register dedicated to the spelling of location names: "Sentralt Stedsnavnregister" ("Centralized Placename Register"). This register is maintained by The Norwegian Mapping Authority and contains 950 000 placenames with a total of 1 112 000 spellings.
Through this register I found information about "Norske Gaardnavne" ("Norwegian Farm Names"), a 19 volume set of books by Oluf Rygh published from 1897 to 1924. This books have been digitalized, and I found that Spilleren Farm in Meløy was spelled Spilderen here (and located in Mælø): http://www.dokpro.uio.no/perl/navnegransking/rygh_ng/rygh_soek.prl?s=n&AMT=&start=S%F8k&HERRED=&SOGN=&GNAVN=spilderen&GNR=&LITTREF=&REFORDF=&BIND=&SIDE=&SOEKESTRENG=&med_amt=on&med_herred=on&med_sogn=on&konkordanse_streng=hurtigliste&sort_tfunn=-&sort_amt=1&sort_herred=2&sort_sogn=3&sort_gard=4
I couldn't find Spilderen or Spilleren in "Sentralt Stedsnavnregister", but many related names still exist in Meløy. Like Spilderdalen (Spilder Valley), Spilderdalselva (Spilder Valley River/Creek), Spilderhesten (Spilder Horse?!), Spildervika (Spilder Bay), Spilderbukta (also Spilder Bay) and Spildervatnet (Spilder Lake).
I think you are really asking how to verify the location of the event. This is more important than deciding which spelling to use. Scale and accuracy are important considerations.
Historical records identify where an event occured using a place name or description of the location. The place name may be very specific e.g. a house name or street address, but often is more general e.g. a parish, town and can be quite vague e.g county, district. A specific location can usefully be described using geographic co-ordinates to an accuracy of a few metres. Administrative units are better described using a polygon that covers the area of the jurisdiction, so that spurious accuracy is not implied. A gazeteer is essentially an index of labels on a map, which give the label name (e.g. a hamlet, town, region) and the central co-ordinate for the feature, and gives no information on the boundaries of jurisdictions. A critisism of the 'Place Authority' mentioned by A C Proctor is that it does not resolve the limitations of the gazeteer. A better solution would be to map historical jurisdictions. An example of such research is the A vision of Britain website
Current maps, including Google maps, Bing and others can be helpful. Taking the Spilleren Farm, Meløy, Norway (1782) example, I can locate Norway and the island of Meloy. Wikipedia has an article on the modern jurisdiction of Meloy (a municipality) and gives co-ordinates 66°47′17″N 13°40′33″E. So, I am reasonably confident that this is the general area. Finding the location of a farm is more problematic as feature this small are often only named of large scale maps. Names of farms can persist for long periods, so may be included in a local gazeteer or maps. You should not assume that the place name is no longer in use before looking at a map of appropriate scale.
(Yes I know it is an old question...)
It can be helpful to understand how spelling has changed over time, to know what to search for.
In the example from Norway we have Spilleren in Meløy. Meløy has the modern spelling of the word island, "øy". In the old Danish spelling used in Norway during the union (up to 1814, and beyond) it would be Melø. (As in the link Sylling provided).
Spilleren is now from what I see spelt Spildra. I'm not sure why ll has changed to ld, it usually goes the other way, but anyway this is just variants of the same. Same thing with nd, it can be nn.
And the ending -en and -a are the same, -en being the older and -a being modern/colloquial/dialectical. It means "the" so Spilleren is The Spiller.
In the modern map at http://kart.gulesider.no/?q=nedrespildra we see Nedre Spildra (Lower Spildra) and Øvre Spildra (Upper Spildra) so the farm seems to have been divided.
Possibly Spildra is originally the name of the river. We also see in the map Spilderdalen (the Spilder valley), Spildervatnet (the Spilder lake, could also be -vannet or -vandet in old spelling), and more.
I guess it boils down to the fact that knowledge of the language and its history is very helpful.
PS: Here is a a video of the area: https://www.youtube.com/watch?v=-jdOdyFOl2g
I endorse Tom's suggestion that Google provides a great suite of tools for this. My preferred entry point is Google Earth because I know that the alternatives offered to my first attempt at spelling the name will be places (and not animals or people or song titles; as can happen in plain vanilla search).
For example, entering Mel caused Google Earth to offer me a choice of Meloy (Norway) Melbourne (Australia) and Melaka (Malaysia) immediately (except it knows the correct nordic character to use in place of "o"!).
I became a convert when entering "Gramz" got me both the village (Gramzow) in what was Brandenburg from which my ancestors came, and the street here in Australia named for their old home!
Once you have the current location pinpointed, you have a solid basis for researching previous names or relationships to nation states.
I have agonized over this exact question myself. In some cases a "place" has changed names 4 or 5 times in the past 200 years, not to mention that there are local language variations and "official" or national names... naming a place often could get out of hand. In addition, these geographic areas are historically and politically unstable, so the name could change in the foreseen future. The short of it all is that in the past couple years I'm concentrating on documenting the coordinates of a place (lat and long) rather then the names. This method will be least impacted by time, and if someone wanted to visit "the place" 500 years from now they most likely would have the technology to do so. Not only that, if I or someone else visit "a place", a GPS can establish the coordinates to the nearest meter! (And I can easily look up the exact place using an online mapping service -- like Google Earth.)
Ask Google and Wikipedia to be your best friends. I have solved essentially all of my place problems by starting out at Google which nearly always takes me to a Wikipedia article with the information I need. Rarely have I had to resort to foreign language gazetteers or old atlases.
