Mapping Path Extensions for easily getting the correct Paths in .net projects. Idea taken from ServiceStack.

PathUtilities.cs

using System;
using System.IO;

/// <summary>
/// Mapping Path Extensions 
/// </summary>
/// Gist Url: https://gist.github.com/KyleGobel/4b0f2b93014cae7bb52b
public static class PathUtilities
{
    private static string MapAbsolutePath(string relativePath, string appendPartialPathModifier)
    {
        if (!relativePath.StartsWith("~")) return relativePath;

        var localAssembly = (typeof (PathUtilities).Assembly.EscapedCodeBase);
        var assemblyPath = Path.GetDirectoryName(new Uri(localAssembly).LocalPath);
        var hostDirectoryPath = appendPartialPathModifier != null
            ? assemblyPath + appendPartialPathModifier
            : assemblyPath;

        return Path.GetFullPath(relativePath.Replace("~", hostDirectoryPath));
    }

    /// <summary>
    /// Maps path of a file in a self-hosted scenario (assumes static content is copied to /bin/)
    /// </summary>
    public static string MapAbsolutePath(this string relativePath)
    {
        return MapAbsolutePath(relativePath, null);
    }

    /// <summary>
    /// Maps path of a file in an Asp.Net hosted scenario (assumes roots is parent of /bin/)
    /// </summary>
    public static string MapHostAbsolutePath(this string relativePath)
    {
        return MapAbsolutePath(relativePath, string.Format("{0}..", Path.DirectorySeparatorChar));
    }

    /// <summary>
    /// Maps path of a file in a VS Project (assumes root is 2 levels above /bin/)
    /// </summary>
    public static string MapProjectPath(this string relativePath)
    {
        return MapAbsolutePath(relativePath, string.Format("{0}..{0}..", Path.DirectorySeparatorChar));
    }
}