I'm pretty new to ArcGIS and have taken the few starter tutorials but I'm still not clued up enough on the vocabulary to know how to google for answers!
Basically I'm having 3 issues:
1. When copying and pasting new layers (maybe not called layers, just individual polygon files) within a .mxd I cannot edit the copy without affecting the original - why is this and how do I change it?
2. Secondly, even though I saved my .mxd file under a new name, the data source (?) must have remained the same because all edits made to my new .mxd file were also in the original - once again why? and how do I change this?
3. I'm struggling with the difference between a .mxd and .gdb. I understand the former is a file produced by Arcmap but I really want to extract the data and save the different files so they are more mobile like in a geodatabase - whenever I try to extract the data using ArcMap it says the output is not valid, is there a specific format required?
Understandably I'm very frustrated as I deleted some information in my copies and have now permanently lost the data. Thank heavens for backups.
Also I apologise if these are very obvious problems and if there is a page you could direct me to, that would be fantastic!
1) When you copy and paste a layer within an mxd, the information comes from the same data source. This is why both layerss change. It is like adding the same layer to your map twice.
If you want an actual copy of your layer: Add the layer to an MXD, right-click the layer in your table of contents, click Data -> Export Data... This will prompt you to name the new layer and where you want to save it. Where it says "Output feature class:" click on the folder icon, change the "Save as type:" to "File and Personal Geodatabase feature classes" and then navigate to your geodatabase. Double click the geodatabase and choose a name for your new layer. Once you set it up, click Save and hit OK it will create a copy and ask you if you want to add the copy to your MXD, now you have 2 different layers with 2 different data sources.
2) When you save an MXD it will only save what you have changed visually in your map. It is just a "area" to perform your edits in. Thats why even if you save it under a different name it will still hold your layers. Again my answer to number 1 should fix this issue.
3) An MXD is a workspace for you to Edit Data, make pretty maps, analyze... A geodatabase houses the data you work with. Kinda like a grocery store is your MXD and the items you sell in it are your layers. Sometimes items are within a carton, that is your geodatabase. Even if you rename your store (MXD) the items inside (your layers) will still be the same. :)
All three of your issues are related to a single root cause. Unlike the CAD (computer aided design) world, where data draws itself on the canvas (and copying a layer makes a clone of the previous data), in the GIS world, data is something that is manipulated or drawn. This makes for two separate sets of resources, Data and Rules.
The ArcMap drawing document (.mxd) is the rulebase by which data (.shp,.gdb,.sde,...) is represented. In order to modify file geodatabase data, while preserving the previous version, you must make an explicit copy of the data (Export, or any of dozens of other ways), make the copy the active edit layer, and edit that. Anything else may corrupt your original data.
The nice part of the GIS model is that data doesn't get trapped in documents. It can be shared by different applications for different purposes, and different renderers can be applied to make the same data available to different purposes, without making dozens of copies of the same features (which would then need to be reconciled when edits are necesary).
Of course, because the rules are partitioned from the data, you can quickly get yourself in trouble if you fail to move the data at the same time you move the rules (this is one of the reasons why enterprise geodatabases are popular -- they provide a single repository, accessible by the entire organization for data resources). There are tools (Properties... Source) to re-associate layers with data which is no longer at the previous path, so keep an out for exclamation points in layers which no longer render.
Once you internalize this difference between CAD and GIS, you'll never experience these sorts of issues again.