Felseth
This tutorial is a response by some to see the techniques I used in the Felseth map turned into a tutorial. I've spent some time in that file trying to figure out which layers and effects mattered and reduced it to just a few. I hope that you get the same results as I do when you attempt these steps to build a pseudo realistic terrain.

Source Tutorials
Firstly I'd like to point out that I didn't come up with these techniques in a vacuum. I ripped them off from these guys (possibly some others, but mainly these three). They deserve all the credit:
http://www.cartographersguild.com/co...e-in-Photoshop
http://oldguygaming.com/adding-reali...lines-to-a-map
http://www.photoshoproadmap.com/Phot...-in-photoshop/

Height Map

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I've found the following steps consistently create a nice looking height map:
  1. File > New...
    • Width: 10 inches
    • Height: 7 inches
    • Resolution: 300 pixels/inch
    • Color Mode: RGB Color / 8bit
    • Background Contents: White
  2. Edit > Fill...
    • Use: 50% Gray
    • Mode: Normal
    • Opacity: 100%
  3. Layer > Duplicate Layer...
  4. Filter > Render > Difference Clouds
  5. Set the layer style to Overlay and Opacity to 25%
  6. Layer > New > Layer...
    • Mode: Overlay
    • Opacity: 25%
  7. Choose the Gradient Tool from the tool bar
  8. Set the gradient pattern to black and white
  9. Pick the Radial Gradient option
    • Mode: Difference
  10. Click and drag randomly around the layer creating patterns
  11. Layer > New> Layer...
    • Mode: Overlay
    • Opacity: 100%
  12. Click and drag randomly around the layer creating patterns
  13. Filter > Render > Difference Clouds
  14. Layer > New > Layer...
    • Mode: Overlay
    • Opacity: 100%
  15. Click and drag randomly around the layer creating patterns
  16. Select all of those layers and right click > Convert to smart Object
  17. Rename this layer to 'Height Map'
  18. Save your file


Creating the Shore Line

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  1. Layer > New Adjustment Layer > Levels
    • Set the Input Levels to 59 and 61
    • Adjust them both up or down to reduce or increase the amount of land to water you want (white will be land, black will be water).
  2. Layer > New > Layer...
  3. Rename this Layer to 'Shore Line'
  4. Select > Color Range...
  5. Select: Highlights
  6. Edit > Fill...
    • Use: White
  7. Delete the Levels Adjustment Layer
  8. Layer > Duplicate Layer...
  9. Rename this Layer to 'Land Mass'
  10. Layer > Group Layers...
  11. Rename the group to 'Land'
  12. Select the bottom three layers
  13. Layer > Group Layers...
  14. Rename the group to 'Ocean'
  15. Save your file


Creating the Ocean

  1. Select the layer named 'Shore Line' in the 'Ocean' group
  2. Layer > Layer Style > Outer Glow...
    • Blend Mode: Color Dodge
    • Opacity: 100%
    • Set the colour to white
    • Technique: Precise
    • Size: 2px
  3. CRTL + Left Click the 'Shore Line' layer if the shore line is not currently selected
  4. Layer > New > Layer...
    • Opacity: 50%
  5. Select > Modify > Expand...
    • Expand By: 25 pixels
  6. Select > Inverse
  7. Edit > Fill...
    • Use: Black
  8. Layer > Layer Style > Outer Glow...
    • Blend Mode: Normal
    • Opacity: 100%
    • Set the colour to black
    • Technique: Precise
    • Size: 20px
  9. Select > Inverse
  10. Layer > New > Layer...
    • Opacity: 50%
  11. Select > Modify > Expand...
    • Expand By: 50 pixels
  12. Select > Inverse
  13. Edit > Fill...
    • Use: Black
  14. Layer > Layer Style > Outer Glow...
    • Blend Mode: Normal
    • Opacity: 100%
    • Set the colour to black
    • Technique: Precise
    • Size: 50px
  15. Select > Inverse
  16. Layer > New > Layer...
    • Opacity: 50%
  17. Select > Modify > Expand...
    • Expand By: 50 pixels
  18. Select > Inverse
  19. Edit > Fill...
    • Use: Black
  20. Layer > Layer Style > Outer Glow...
    • Blend Mode: Normal
    • Opacity: 100%
    • Set the colour to black
    • Technique: Precise
    • Size: 20px
  21. Select the shape tool from the tool bar (U)
  22. Draw a shape of any size
  23. Right Click the vector mask for the newly created layer and choose 'Disable Vector Mask'
  24. Double Click the layer and set the colour to RGB value: 26, 40, 87
  25. Set the layer Opacity to 50%
  26. Save your file


Setting the Land Colour

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  1. Select the Layer called 'Height Map'
  2. Layer > Duplicate Layer...
  3. Move the new layer the 'Land' group above the 'Land Mass' layer
  4. Hold down ALT and left click along the bottom of the 'Height Map copy' layer
  5. Layer > New Adjustment Layer > Gradient Map...
    • The exact positions of the gradient colours will depend on the gray scale values of your height map
    • The five colours of the Gradient Map from Left to Right are:
      • RGB: 199, 184, 157 (Sand)
      • RGB: 133, 150, 101 (Grass)
      • RGB: 84, 99, 42 (Forest)
      • RGB: 117, 100, 93 (Hills)
      • RGB: 157, 144, 118 (Peaks)
  6. Hold down ALT and left click along the bottom of the Gradient Map layer
  7. Save your file


Relief Map Detail

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  1. Select the 'Height Map' Layer
  2. Select > All
  3. Edit > Copy
  4. Switch to the Channels window
  5. Press the Create New Channel button to create a Alpha channel layer
  6. Edit > Paste...
  7. Switch back to the Layers window
  8. Select the 'Gradient Map' layer
  9. Layer > New > Layer...
  10. Edit > Fill...
    • Use: 50% Gray
  11. Filter > Render > Lighting Effects
    • Light type: Directional
    • Intensity: 21
    • Gloss: 0
    • Material: 71
    • Exposure: 0
    • Ambience: 0
    • Texture Channel: Alpha 1
    • Height: 100
  12. Change the layer Style to Overlay
  13. Rename the layer to 'Hills'
  14. Save your file


Colour Adjustment Layers

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  1. Close and select the 'Land' group
  2. Choose the Shape tool (U)
  3. Click and drag anywhere on the image to create a shape (this should be above the 'Land' group)
  4. Right click the shape vector mask and choose 'Disable Vector Mask'
  5. Double click the layer and set the layer colour to RGB: 242, 231, 209
  6. Set the layer style to Multiply
  7. Layer > New Adjustment Layer > Hue/Saturation
    • Hue: -14
    • Saturation: -20
    • Lightness: +6
  8. Save your file


This is just the base for a map. From here you will need to add trees, roads, rivers and other details.

If you find anything that's hard to follow let me know and I'll clean it up as best I can.