How do I make a color wider?

[kbrmaster]

I have a map with yellow roads, green terrain, black borders and blue water. I want to make my roads wider.

My roads are yellow. Is there a way to select every yellow pixel in my image and add an adjacent yellow pixel to everything in the image with that color?

A zoomed in view of the larger map I am dealing with is attached.

[Semaphoric]

Use Select > Color Range to select all the yellow pixels. Press Q to enter Quick Mask mode. With the Quick Mask channel active, run Filter > Other > Maximum. Press Q to return to Standard Mode. Set the Foreground color to Yellow, and fill, then deselect.

This is sort of a brute-force way, but you could add refinements like extra layers with various blending mode and such

[HOSTVN]

Thanks you, it applies to me.

HOSTVN

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[Norman Sanders]

Unfortunately no image accompanied your post so I have to assume that you can make a selection of the yellow  road. In that case, make that yellow your Foreground Color. Then make a Selection of the road. With the marching ants showing, choose Select > Modify > Expand and enter 1 or more pixels to expand the Selection. Follow that with Edit > Fill and fill with the Foreground color. 

[c.pfaffenbichler]

Could you please post (a part of) the image in question? 

[kbrmaster]

It must have failed to attach. Thank you all for the suggestions. I will give it a try tomorrow. 

[c.pfaffenbichler]

Please post the actual image (or part of it), not a rotated and therefore damaged version. 

Edit: It actually looks like a photograph of the screen …