Here is the map of Johto/Kanto in HeartGold/SoulSilver!

Combined News

Scans from CoroCoro shows that

1) There is a new artwork for Prof. Elm, Silver, male and female Team Rocket Grunt.
Pictures of Prof. Elm's Lab, Slowpoke Well, Cherrygrove Town, Ruins of Alph and the Johto Radio Tower. Also, the first battle with Silver. (battle screens same as Platinum)

2) The new artwork of the Johto map shows that players can head east to Kanto and it also shows Route 28 and Mt. Silver. It also shows a new area west of the National Park. An artwork for Ecruteak City is also shown, including the Tin and Brass Towers.

3) The Pokédex has been redesigned. Pink for Kotone and red for Gold. A battle between Gold and Silver, is also seen, revealing Gold's new back sprite and Silver's new sprite.

4) All Pokémon will follow you. Trainers can talk to them to know their feelings. You also can collect accessories from them, similar to in Amity Square (in DPPt). Shiny Pokémon will remain Shiny.

5) Another scan shows the newly designed Pokédex, PC Box and the Pokémon Status screen which use the touch screen more in navigation. The redesigned interface of the bag also utilizes the same feature.

6) Another scan shows how HeartGold and SoulSilver will look like when a Pokémon is going to be sent to it. One of the screenshots involves Pikachu encountering with a wild Kangaskhan. Wild Pokémon encountered on the PokéWalker are transferable into the two games. Two in-game cut scenes can also be seen with Ho-Oh flying above the Tin Tower and Lugia behind a waterfall in Whirl Islands, which will be the same as the cut scenes of the Weather trio in Sootopolis City in Pokémon Emerald.

7) The weather trio of Hoenn, Groudon, Kyogre and Rayquaza in the HGSS at Level 50. After defeating the Elite Four of Johto, and getting the Blue/Red Orb, Kyogre will be in HeartGold, Groudon in SoulSilver in Hidden Tower, next to Cianwood City. Once Groudon and Kyogre are together, and collected Light Green Orb, Rayquaza will appear.

That's all the information on HeartGold/SoulSilver from 10^th to 13^th June.

My Pokémon blog.
News reporting depending on Bulbapedia and Serebii. (And maybe Psypokes)
With effects from 10 June.