title: Change labeling of continuous scale bar ggplot
body: <p>I'm not even sure if this is possible to do with a continuous scale bar but I give it a try ;)</p>
  <p>I have this data:</p>
  <pre><code>return_cluster
      year variable      value
  1   1988       V1   1.721150
  2   1989       V1   5.288607
  3   1990       V1  63.355563
  4   1991       V1  47.516021
  5   1992       V1  48.766120
  6   1993       V1  20.463455
  7   1994       V1   1.116961
  8   1995       V1   1.804225
  9   1996       V1   5.159672
  10  1997       V1   2.342435
  11  1998       V1   1.831826
  12  1999       V1   2.916135
  13  2000       V1   2.096115
  14  2001       V1   2.205473
  15  2002       V1  97.766868
  16  2003       V1   1.395028
  17  2004       V1  14.778782
  18  2005       V1  21.626368
  19  2006       V1 335.569275
  20  2007       V1   2.577229
  21  2008       V1  46.794667
  22  2009       V1  18.456694
  23  2010       V1  28.347202
  24  2011       V1   1.754569
  25  2012       V1   1.967250
  26  2013       V1   1.355391
  27  2014       V1   2.310848
  28  2015       V1   1.236857
  29  2016       V1  72.404651
  30  2017       V1 327.830361
  31  1988       V2   1.602976
  32  1989       V2 144.354881
  33  1990       V2  98.927558
  34  1991       V2  47.287984
  35  1992       V2  47.254139
  36  1993       V2  50.085161
  37  1994       V2   1.519317
  38  1995       V2   1.290500
  39  1996       V2  27.165630
  40  1997       V2   3.708591
  41  1998       V2   2.900900
  42  1999       V2  32.971143
  43  2000       V2   1.783584
  44  2001       V2   1.556819
  45  2002       V2   2.397101
  46  2003       V2   2.100313
  47  2004       V2   1.878331
  48  2005       V2  59.814862
  49  2006       V2 561.607269
  50  2007       V2  18.060577
  51  2008       V2  24.921608
  52  2009       V2  25.684559
  53  2010       V2  30.211938
  54  2011       V2  14.210188
  55  2012       V2  19.619167
  56  2013       V2   1.614514
  57  2014       V2   9.915848
  58  2015       V2  46.625465
  59  2016       V2   2.088176
  60  2017       V2  27.044079
  61  1988       V3   3.491779
  62  1989       V3   2.808945
  63  1990       V3  91.647147
  64  1991       V3   3.398350
  65  1992       V3  50.143573
  66  1993       V3 183.457528
  67  1994       V3   1.281821
  68  1995       V3   1.875897
  69  1996       V3 371.005217
  70  1997       V3   2.425475
  71  1998       V3  18.015665
  72  1999       V3   1.419050
  73  2000       V3  47.724070
  74  2001       V3   1.143962
  75  2002       V3   1.951659
  76  2003       V3   2.676810
  77  2004       V3   2.597871
  78  2005       V3  69.679082
  79  2006       V3   7.110426
  80  2007       V3  47.511509
  81  2008       V3   1.880928
  82  2009       V3   1.988084
  83  2010       V3  83.713620
  84  2011       V3  31.541859
  85  2012       V3   1.897654
  86  2013       V3   2.341847
  87  2014       V3   3.733591
  88  2015       V3  23.842150
  89  2016       V3  13.638751
  90  2017       V3   1.712088
  91  1988       V4   1.486628
  92  1989       V4   1.407240
  93  1990       V4  26.211749
  94  1991       V4  67.534555
  95  1992       V4  92.307045
  96  1993       V4   3.528735
  97  1994       V4  17.328366
  98  1995       V4   4.674465
  99  1996       V4  88.268235
  100 1997       V4 132.922890
  101 1998       V4   4.439413
  102 1999       V4   1.401003
  103 2000       V4   2.812608
  104 2001       V4   1.526576
  105 2002       V4   4.921232
  106 2003       V4  51.542854
  107 2004       V4   3.860508
  108 2005       V4   2.243960
  109 2006       V4   2.507551
  110 2007       V4  18.467204
  111 2008       V4   4.301163
  112 2009       V4   1.188909
  113 2010       V4 186.013334
  114 2011       V4 260.879110
  115 2012       V4   1.833610
  116 2013       V4  69.432973
  117 2014       V4   9.092139
  118 2015       V4   1.710509
  119 2016       V4   1.442288
  120 2017       V4  21.648317
  121 1988       V5   1.124042
  122 1989       V5   5.834290
  123 1990       V5  18.423492
  124 1991       V5  71.584537
  125 1992       V5  48.946872
  126 1993       V5   3.994614
  127 1994       V5   1.375991
  128 1995       V5   1.389525
  129 1996       V5   4.434723
  130 1997       V5   3.192515
  131 1998       V5  57.507683
  132 1999       V5   1.107362
  133 2000       V5   1.440586
  134 2001       V5   1.216205
  135 2002       V5   1.601559
  136 2003       V5   4.691851
  137 2004       V5   2.350900
  138 2005       V5   4.148232
  139 2006       V5   2.560688
  140 2007       V5 161.408504
  141 2008       V5   1.526090
  142 2009       V5   2.304330
  143 2010       V5   3.424447
  144 2011       V5 251.419437
  145 2012       V5   1.477274
  146 2013       V5   1.403403
  147 2014       V5   2.473882
  148 2015       V5   1.708639
  149 2016       V5   2.773274
  150 2017       V5   6.344827
  151 1988       V6   1.518616
  152 1989       V6  58.778503
  153 1990       V6   2.912868
  154 1991       V6   2.684705
  155 1992       V6  24.784557
  156 1993       V6  47.099474
  157 1994       V6   1.901775
  158 1995       V6  16.253749
  159 1996       V6  11.504747
  160 1997       V6   2.819182
  161 1998       V6  19.980632
  162 1999       V6   1.390191
  163 2000       V6   4.207280
  164 2001       V6   1.332001
  165 2002       V6   3.676687
  166 2003       V6 208.344203
  167 2004       V6   4.790638
  168 2005       V6  68.214507
  169 2006       V6 244.268239
  170 2007       V6   8.262237
  171 2008       V6   1.743053
  172 2009       V6  19.925573
  173 2010       V6   2.313235
  174 2011       V6 265.988933
  175 2012       V6   1.549337
  176 2013       V6   1.484683
  177 2014       V6 135.733452
  178 2015       V6   2.846374
  179 2016       V6   1.094535
  180 2017       V6 148.108424
  181 1988       V7   1.686723
  182 1989       V7   7.227748
  183 1990       V7  35.340633
  184 1991       V7  10.835810
  185 1992       V7   2.138298
  186 1993       V7   1.575984
  187 1994       V7  10.129774
  188 1995       V7  50.201159
  189 1996       V7  13.209625
  190 1997       V7   2.184044
  191 1998       V7  16.584965
  192 1999       V7   2.480640
  193 2000       V7   5.299119
  194 2001       V7   1.319700
  195 2002       V7   2.265038
  196 2003       V7 355.111101
  197 2004       V7  21.919797
  198 2005       V7 104.912027
  199 2006       V7 254.276631
  200 2007       V7  49.192583
  201 2008       V7  24.358314
  202 2009       V7  11.218015
  203 2010       V7  14.356157
  204 2011       V7  48.386913
  205 2012       V7   7.390883
  206 2013       V7   4.089435
  207 2014       V7   1.693219
  208 2015       V7 297.646638
  209 2016       V7   1.670901
  210 2017       V7  29.193866
  211 1988       V8   4.291061
  212 1989       V8  10.147915
  213 1990       V8  45.486480
  214 1991       V8  68.942930
  215 1992       V8  16.576701
  216 1993       V8  11.493921
  217 1994       V8   8.940650
  218 1995       V8  47.943372
  219 1996       V8   7.088878
  220 1997       V8  11.432932
  221 1998       V8  76.057542
  222 1999       V8   1.912122
  223 2000       V8   2.881820
  224 2001       V8  17.467523
  225 2002       V8   1.830679
  226 2003       V8 353.781607
  227 2004       V8   3.107457
  228 2005       V8  35.021645
  229 2006       V8  64.324620
  230 2007       V8  59.491304
  231 2008       V8  24.755776
  232 2009       V8   2.546088
  233 2010       V8   1.617441
  234 2011       V8   3.438010
  235 2012       V8  12.320183
  236 2013       V8  13.426661
  237 2014       V8   1.687504
  238 2015       V8 109.999377
  239 2016       V8   5.236363
  240 2017       V8  14.251569
  241 1988       V9  11.798883
  242 1989       V9  38.970656
  243 1990       V9  95.412293
  244 1991       V9 162.053168
  245 1992       V9  10.486107
  246 1993       V9  62.022276
  247 1994       V9   1.305770
  248 1995       V9  46.413613
  249 1996       V9  10.403840
  250 1997       V9  68.976595
  251 1998       V9  10.699454
  252 1999       V9   2.762492
  253 2000       V9  11.052923
  254 2001       V9   2.285492
  255 2002       V9   2.210362
  256 2003       V9 363.602498
  257 2004       V9  49.067139
  258 2005       V9  21.810117
  259 2006       V9  10.043886
  260 2007       V9  23.549936
  261 2008       V9  24.546635
  262 2009       V9 157.500968
  263 2010       V9   2.152319
  264 2011       V9   2.684216
  265 2012       V9   9.913968
  266 2013       V9  10.366976
  267 2014       V9   3.802875
  268 2015       V9  62.889429
  269 2016       V9  36.761245
  270 2017       V9  27.634371
  271 1988      V10  24.666011
  272 1989      V10 187.050844
  273 1990      V10  61.212670
  274 1991      V10  23.364418
  275 1992      V10  18.781973
  276 1993      V10   1.101492
  277 1994      V10   4.368106
  278 1995      V10  78.504693
  279 1996      V10   2.042534
  280 1997      V10 208.185547
  281 1998      V10   9.015323
  282 1999      V10   1.846591
  283 2000      V10   1.535912
  284 2001      V10  24.826558
  285 2002      V10  10.650948
  286 2003      V10 207.507455
  287 2004      V10  20.041347
  288 2005      V10 101.049600
  289 2006      V10  50.859651
  290 2007      V10  41.764536
  291 2008      V10  18.482884
  292 2009      V10 344.989241
  293 2010      V10  36.112390
  294 2011      V10  78.213088
  295 2012      V10   1.848186
  296 2013      V10   2.696125
  297 2014      V10  56.530760
  298 2015      V10  48.419746
  299 2016      V10  87.035051
  300 2017      V10  26.644928
  301 1988      V11  70.310367
  302 1989      V11 174.213909
  303 1990      V11  15.481841
  304 1991      V11  15.031165
  305 1992      V11  23.790369
  306 1993      V11   1.751277
  307 1994      V11   3.166003
  308 1995      V11  57.540285
  309 1996      V11   2.287525
  310 1997      V11  20.564880
  311 1998      V11  17.683897
  312 1999      V11   1.706362
  313 2000      V11   1.411072
  314 2001      V11   9.545351
  315 2002      V11   5.165300
  316 2003      V11  12.511814
  317 2004      V11  54.369030
  318 2005      V11 324.799491
  319 2006      V11  18.882354
  320 2007      V11 111.124844
  321 2008      V11   1.890256
  322 2009      V11  18.330233
  323 2010      V11   1.681225
  324 2011      V11 268.381319
  325 2012      V11   1.590532
  326 2013      V11   1.217613
  327 2014      V11   1.221466
  328 2015      V11 172.429858
  329 2016      V11  18.171812
  330 2017      V11  13.392772
  331 1988      V12  13.568733
  332 1989      V12 283.648545
  333 1990      V12  28.669739
  334 1991      V12  54.023489
  335 1992      V12  12.933720
  336 1993      V12   5.902544
  337 1994      V12  12.104002
  338 1995      V12  53.059435
  339 1996      V12   1.565862
  340 1997      V12  23.069261
  341 1998      V12  34.233273
  342 1999      V12   6.442077
  343 2000      V12   7.617126
  344 2001      V12  66.787312
  345 2002      V12   1.324712
  346 2003      V12  27.446611
  347 2004      V12  82.908726
  348 2005      V12 364.147874
  349 2006      V12  39.927251
  350 2007      V12  54.989735
  351 2008      V12   2.448610
  352 2009      V12   5.168975
  353 2010      V12   1.674610
  354 2011      V12  11.135477
  355 2012      V12   3.013439
  356 2013      V12   5.467428
  357 2014      V12   2.414924
  358 2015      V12 101.976833
  359 2016      V12 209.803373
  360 2017      V12  18.037623
  </code></pre>
  <p>I plot it with this code:</p>
  <pre><code>ggplot(return_cluster, mapping = aes(x = variable, y = year, fill = value)) +
    geom_raster() +
    scale_y_continuous(trans = &quot;reverse&quot;) +
    scale_fill_gradientn(colors = c(&quot;blue4&quot;, &quot;dodgerblue1&quot;, &quot;green3&quot;, &quot;yellow&quot;, &quot;red&quot;), limits = c(0,500), name = &quot;value&quot;, breaks = c(10,20,50,100,500))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/daCI4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/daCI4.png" alt="enter image description here" /></a></p>
  <p>As you may be already noticed I changed the label interval of the scale bar. But I try to achieve, that only the names of the labels change but that the distance between each label stays the same as if I had used the default one with <code>breaks</code> at <code>100, 200, 300, 400 and 500</code>.</p>
  <p><a href="https://i.stack.imgur.com/OstDy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OstDy.png" alt="enter image description here" /></a></p>
  <p>So the from top to bottom the black lines should represent 500, 100, 50, 20, 10</p>