Open the image you just created in Photoshop, this time in Illustrator, and select it; then apply the Mosaic filter, located under Filter, Create, Object Mosaic. I set Number of Tiles to 60 for both Width and Height, as detailed in Figure 4. Check the Delete Raster option; otherwise, in the next step, you might end up wondering what all the ugly, jaggy shapes arethey're actually the original bitmap showing through.
Leave New Size set as is, to match the dimensions of your original image, unless you want it to be larger or smaller than it is now. Leaving Tile Spacing set to 0 will cause the edges of the tiles to touch, which is what you want. Click OK to create the mosaic. If it doesn't look right, undo it and make changes until you're happy with the results.
Next, ungroup the mosaic so you have access to the individual blocks that comprise the image. Select one of the white blocks, and then choose Select, Same, Fill Color to select the rest of them. Delete all of the white squares; they'll just interfere with the effects you may want to apply later in Photoshop. Planning ahead is one of the best habits you can develop.
Figure 4 Object Mosaic filter settings.
Delete any blocks that throw off the map's accuracy, and add blocks anywhere they're missing. Take a screen capture of Illustrator and paste it into Photoshop, overlaid on top of the raster map so you can see which blocks need to be removed or added. Lower the pasted layer's opacity to around 70% so you can see both the original and the mosaic at once. Remove unneeded blocks in Illustrator, and copy and paste blocks where they're missing. Then take another screen capture and compare again.
When everything is to your liking, use the Eyedropper tool to select the correct colors and fill any off-colored blocks. Use the Lasso tool to select large areas that need to be filled. When all the blocks are of uniform color and the map looks like North America rather than an inkblot, it's time to apply the Convert to Shape effect.
Figure 5 Checking where to add and remove blocks in Photoshop.
Figure 6 The map as it appears after adding and removing the appropriate blocks.