Edit a texture.

One reason you might want to modify a texture will probably be to smooth out places where two different textures meet, like where you have made an unusual intersection of a dirt road and an asphalt road and the normal pieces just don’t seem to want to fit quite right. With all your other textures in place, there may be just a few spots that need tweaking. When you paste part of one texture into another one, it is added in a separate layer. You can see the current layer in the Layers Palette. When you are cutting and pasting pieces together, having separate layers is convenient, but when you are ready to draw or apply filters, you need to flatten the image first to combine all those layers.

Now you’re ready to do some editing. Time to jump into an example. In this example, you need to use a few tools that are sitting in your toolbox.
 

1.	The intersection doesn't look quite finished,  I couldn't find the texture I needed to tie together the 3 different road, asphalt, and grass textures.
	Looking at the intersection with the grid applied, it's easy to see the textures that need tweaking.
2.	Load the edge of your asphalt road, and the segment of dirt road into Photoshop and convert to RGB mode.   (I make a duplicate of any texture I’m working on, then close the original without saving any changes so I know I won’t make any un-reversable mistakes, then do all editing on just the duplicate files. From the menu, select Image > Duplicate.)   Resize the frames and zoom in a little to make them comfortable to work on.  It's best to have the frames a little bigger than the images themselves, if you run over a little while cutting and pasting, the excess is just clipped off.
3.	When you combine the two textures, you want to maintain the grass edge alignments of both the original textures so you can reuse your new texture in other places where these roads meet.  The red lines show the edges you want to maintain.
4.	To select the area you want to copy, use your polygonal lasso tool (the lasso with the straight edges) to select the black boxed area.  Its ok to go outside the picture, the tool will only grab the image itself.
5.	After selecting with the lasso, you will see a blinking line where your selection is, if you screw up the selection, just start over with lasso.
6.	When you have about half the image selected, from the menu select Image > Copy (Ctrl+C).
7.	Next select the other image.  From the menu select Image > Paste (Ctrl+V).
8.	A floating image of the dirt road then appears in the asphalt road image. The floating image is contained in a new, separate layer.  Select the Move Tool (the little arrow in the top right of the tool box) and slide the floating dirt road image into place, maintaing the edges of both images.
9.	The area in the red box is the most critical alignment area.  Can you see how there is grass all in that corner?  This way you know an asphalt/grass, dirt/grass, or just plain grass texture can fit up against there ok.  Next, to flatten the texture, from the menu, select Layer > Flatten Image.  Then use the Smudge tool (the pointing finger in the tool box) to kind of soften the lines between the textures you've pasted.
10.	This single new texture can be mirrored and turned to fill in the gaps in all four places.
11.	In more general terms, anytime you are making two or more textures meet, you want to work it out so the smudgy lines between them meet at about half way along the edge of the texture image, that way when you lay different textures beside each other that smudgy line meets up with the other smudgy lines. The most basic thing is to split the texture in half then smudging the line between dirt and grass. Or you might need to make some diagonal tiles if your road runs off at a 45 degree angle.
12.	When you are done tweaking, you are ready to Save you new texture so you can try it out.